What is it about INFPs that makes them doubt their type? It happens so often, sounds almost like a prerequisite to be one.
A lot of great advice has already been said here, but I'd also like to ask, do you know your enneagram type? As BlackCat said earlier, most INFPs are 4s, and many profiles seem biased towards that type. We may be INFPs, but we're not all the same--we're still individuals. What makes us the same is how our functions work, and different functions are stronger in different INFPs. For example, your Te seems far better than mine; your opening post was very coherent and to-the-point.
And here's a hug. Low self esteem doesn't have to last forever. Having gone through it myself, I just want to let you know that INFPs especially have a problem with obsessing over negative feelings. But on the flip side? The positive ones come off so much stronger, too. Imagine feeling just as intensely as you do, right now, but because you feel wonderful inside. It's the Fi, I think. It makes us so vulnerable to our emotions sometimes. So you're not alone!
And one more thing. Ti seems scary, but it's not. If you meet the right Thinkers, it can be a lot of fun. You can gain a lot from it.