I have a few questions to atheists, before I become one.

[Tonus]

But every time I read or watch a video explaining why atheism is true,

This could be a part of the problem. Do not approach atheism from this end, because you cannot "explain why atheism is true." Atheism simply describes a lack of belief in the existence of god. For some people this implies a certainty that all gods do not --and perhaps cannot-- exist, for others it usually means that the gods that they have learned about are not convincing enough to seem real.

Examine your beliefs and your faith. What is it that is causing you doubts? Think on those things and try to understand them. Do not just try to "disprove" them or point yourself in one direction (theism) or the other (atheism) because then bias will lead you to conclusions now that you might have doubts about later. Try to figure out why you believe as you do. The key to figuring out which is "right" is to get to know yourself better.

You should definitely discuss this with your psychiatrist, as I have no clue how your OCD affects your ability to research and work through such issues.