peace,
Welcome to the forum.
Can you clarify if you having doubts about Islam (capital "I", title of a religion) or islam (small "i", as described in Quran)?
Here is a decent start http//misconceptions-about-islam.com
I guess capital I, but I still need strong evidence to submit (lowercase i).
This might turn out very long, sorry. I am 20, in the USA, in college. Male. I'll have a TL;DR at the end.
Before I was 15, I just followed Islam based on what I thought it was. My parents do not pray, my aunts and uncles drink alcohol openly and proudly, they gamble, they don't fast, they make fun of the deen, etc. I thought Islam was just "Believe in Allah and Muhammad and you're good." When I turned 15, I decided I wanted to learn my religion. If I was already not eating pork, I might as well find out why. At 15, I read the Quran, sirah, books on faith and the history of Islam, and I became knowledgeable on many matters of the deen. I was fully practicing 5 prayers, extra fasts, daily dua, covering my awrah more carefully, growing a beard, avoiding parties with alcohol, music, and free mixing (so all high school parties). I became lonely and isolated, but it was okay because I thought I would be going to jannah and all would be worth it.
Despite being practicing, I always had doubts. If Allah is real and Islam is the true religion, why won't Allah send me a clearer sign? Why aren't my duas answered? What is the proof that Islam is real beyond some vague "scientific miracles" and a linguistic miracle that no one really explains? Biggest of all, I didn't know if the afterlife really existed, and if not, am I living a life of restriction for nothing?
Now at 20, I feel this more than ever. My family smokes weed and drinks alcohol, so all family gatherings are miserable for me. I get made fun of for refraining, I get made fun of for being uptight. I sit there on the couch with hate in my heart toward their alcohol and marijuana, with discontent in my environment. My friends, both Muslim and non-Muslim, also indulge in these things, so parties are also spent with hate in my heart and immense guilt. However, that's not the problem, the problem is that I don't know if Islam is the absolute truth. These doubts, I think, stem completely irrelevantly from my desires. I just want strong proof for the deen to be true in order to ignore my desires. I have stopped praying and offering more fasts, and I have lost my vigor for the deen. I read the Quran in Arabic and English, so I understand it thoroughly, it's just not enough. My fear is that what I consider enough of a proof is too big to happen a clear, direct, huge sign or miracle. Not just a coincidence. It will never happen, because I am not worthy for one, but also because it would defeat the purpose of the test. It would essentially be Allah saying "Islam is the truth, and no other religion is true."
To complicate it, I am bisexual, which might gain me hate on here, but it's a huge influence on my life. Growing up, I never had gay friends, but I developed crushes on guys. Now as a 20 year old, I find myself developing crushes on men, which I can ignore because I also like women, but it feels like a huge burden to ignore my desires. Again, I ask why follow the rules if I don't believe? I desire to drink alcohol and smoke weed like my friends and family do. I desire to not have to be left out at all times. I desire to have a relationship without the immediate responsibilities of a marriage and children. I am willing to give all that up if Islam can be, beyond a shadow of a doubt, proven to be the only truth. My major doubt is that there is no objective, unambiguous proof of Islam, because it defeats the purpose of the test.
Here are my more tangible, though minor, doubts
There is no reason for slavery to not have been abolished, and not a SINGLE argument has satisfied me. Yes, it was an integral part of society, but so was alcohol and polytheism and divination. All were made away with. I recognize slavery in Islam is NOT African-American slavery. Still, I don't understand why the descendants of prisoners of war (who would be the ones enslaved) are also slaves. That's unjust to them.
No matter how you explain it, Aisha's age is incomprehensible. Muhammad was not abusive or a bad husband, but I still can't wrap my head around the best human in history who serves as a role model for all could do that. I know there is wisdom behind it (namely that she served to transmit ahadeeth and sirah), but it doesn't outweigh my repulsion. Any claims that there is scholarly disagreement will not be considered, because the overwhelming evidence points to her being 6.
If Islam is not exclusively for Arabs, why are the laws conveniently based on Arab laws at the time? Literally almost every shari' punishment is based on a law the Arabs used. On the one hand, you can argue that the Quran was sent to the Arabs because Allah's laws aligned with theirs the most. On the other, in all of time, and of all cultures, the best laws were the Arabs' in the 7th century?
The arguments for God and such in the Quran is also clearly based on the Arabs' beliefs at the time. It boils down to you believe in a supreme god named Allah, and you have set up minor gods with Him. Get rid of the minor gods, because Allah is the only god. This is not the model of every religion at all.
There is a lack of awareness of the Americas... the fact that scholars had to invent ways for people living in Alaska to fast and pray shows an absence of awareness. If the Quran was meant for all of mankind, then it should've provided ways for them.
If the Quran is so clearly from God and any sane person would recognize it as the truth, then how is there a test of faith? What is the test? If it's so clearly true, then there is no test. If a professor gave me a test but gave me all the answers, it isn't a test.
Again, these doubts are incredibly minor in comparison to my main one I need a large, tangible proof that Islam is true and that I must obey the commandments to not burn for eternity. I'm so sorry to be arrogant, but I can't keep practicing if I don't know if there's a reason.
TL;DR I taught myself much of Islam, but I never could shake my major doubt, which is the lack of objective proof of an afterlife. I believe in God, but I am unsure if Islam is the truth. I am having trouble practicing Islam in the absence of full faith and conviction.