STEM people: Did any of you struggle hard in undergrad?

I am just struggling lately. I am painfully bad at calculus. I think I'm actually pretty solid on algebra and trig, maybe not too terrible with derivatives, but solving integrals is just... bad. It feels like a big jump in difficulty or complexity from anything I've done in math before.

I'm trying to do more problems. I just bought the Schaum's Outline for Calc for extra practice problems and worked examples. I have a tutor. But for some reason, integration is just... not clicking.

My professors tell me that hard work and determination mean more than "natural talent" or "having a math brain". But when I'm feeling sorry for myself, it sure feels like having a math brain where I can just look at an integral and say, "Oh well of course this is how you solve it" would be great.

Anyway, I want to know, did any of you legitimately struggle as undergrads, then manage to pull it through with hard work and determination? Are there real, actual examples of people who went on to be highly successful in math or physics despite having little/no aptitude?