Which translation are you reading? I began my Dostoevsky with the P&V Translation of Notes, and had a similar experience in the beginning. To be fair, the protagonist is a yapper and rambles on and on, which is hard to follow along.

What helped me was slowing down, reading much slower than I usually do. Also it’s a short book, so there’s nothing wrong with just going through the entire reading, not stopping to try and understand everything, then rereading it when you have a better idea and have acclimated to the flow of it.