Not sure if I have the brain capacity for this

This is the second year of my PhD and I’ve felt and noticed cognitive differences between me and other students, as well as just general dissatisfaction with my lack of cognitive ability. I feel like my brain doesn’t work at a level it should. For example I’ll read papers, and essentially not remember most of it, which makes it very hard to deal with in a paper discussion. I’ll make mistakes with my data and catch it at a later time and have to go back. I typically struggle to think of answers for questions and have a hard time breaking things down to answer them. I’m overall worried for qualifying exams because I don’t have a decent memory and struggle to memorize new concepts. I’m enjoying it but a little concerned for my longevity as a scientist!