What you say is very true of Mother Theresa having doubts. The same was true of every single apostle, disciple, or saint. You can’t approach the dark-night-of-the-soul without having doubts, and you can’t experience God without going through the dark-night-of-the-soul.
The process though is not doubting God, it is doubting “self” and the realization that we are not in control, a necessary step in surrendering to God and finding joy.
There are no atheists in foxholes!
One of my favorite all time quotes was Abraham Lincoln during the Civil War. It was during a National Day of Prayer when a group of Methodist ministers came to visit Mr. Lincoln and said, “We pray that God is on our side.”
Mr. Lincoln replied,”That is not my concern! But that we are on God’s side is my concern!”
I’m always suspicious of believers who claim to have zero doubts about their faith and salvation. That’s not my experience. I wish I could say I never doubt, but sometimes I do.
I arrived at Christianity through the study of scripture. It wasn’t so much an emotional experience as an intellectual decision that Christ was plausible. He made a good case and seemed to have a very good explanation for why the world is the way it is (His parables, especially, are very enlightening).
Christ didn’t leave a lot of wiggle room either. You can either believe He was telling the truth, something that compels one to act, or you can think He lied. He himself didn’t leave any middle ground (contrary to those who think He was a prophet or just a guy with good intentions).
So it comes down to putting trust, call it faith, that Christ was who He said He was. If it turns out that I end up being a fool for Christ, I won’t know it. On the other hand, I hope and pray for mercy and will receive it if He was who He said He was.
BTW, I periodically re-evaluate my decision when doubts arise. I always come back to the realization that I’ve never heard a better explanation than Christ’s.