When doubts arise, we need something solid that we can fall back on to remind of why we have good reason to believe, which a sign is not.
Okay, so what is something solid? I've got nothing.
I think that investigating how we can know that the Bible is true is not something that should be discouraged or something that should shake us to our core, but rather it is something that is healthy that should be encouraged that is vitally important for every Christian to have a solid grasp of, in which many churches have sadly failed to educate us
I'm not too interested in debating the nitty-gritty of the Bible. I'm interested in claims like Moses speaking to God in a burning bush and Jesus coming back from the dead after being buried three days. Why in the world should I believe any of that?
I think this goes back to correctly understanding faith. God gives us faith by putting us in situations where we need to depend on Him.
...except that in situations where I've tried to depend on Him, I come away feeling less and less confident that He even exists.
However, I hope you don't take offense at this, but if wherever you go people are reacting to you in the same way, then the problem might have more to do with you than with them. Again, it is hard for me say whether that is the case without knowing your circumstances, but it might be worth considering whether there are any changes that you should make to improve. Furthermore, if you lose your faith because of how other Christians act, then it might be the case that your faith was not in God, but in other Christians.
Coming from you, I'm not offended. I'm not talking so much about how other people react to me, but to churches in general... the way people treat each other, the way the pastor preaches and interacts with the congregation, the way "outsiders" are treated, bad theology, cult-like vibes, and the like. Frankly I rarely stick around long enough to make friends, and if I do happen to make a few, they end up leaving the church too. Also, the way I see Christians act is a symptom, not a cause. To me, the fact that Christians seem no different than anyone else is proof that there is nothing supernatural happening in their lives. I know that probably seems personal, but there really is no nicer way of putting it.
You could start with one example.
The ongoing thread concerning Mosaic law contains many examples, actually. I haven't posted in it, but a quick skim over the objections to Mosaic law closely mirror my own thoughts.
The Bible doesn't attempt to prove the existence of God, but rather it starts "In the beginning God...", so it is more about answering the question of who God is and what He has done. I don't know if you've heard of William Lane Craig or watched any of his debates, but he gives a few arguments for the existence of the God of classical theism and then gives an argument for the resurrection of Jesus, which is an essentially an argument for the Christian identity of this being. I think Thomas Aquinas makes strong arguments for the existence of God and recommended Edward Feser's book Aquinas if you are somewhat philosophically inclined.
I studied Aquinas a bit in college, but I don't remember much of him. I also come from a background that is highly skeptical of Aquinas' scholasticism, that is Russian Orthodoxy, so I've never been too inclined to go more in-depth. Any arguments in particular you find convincing?