How can I improve at studying?

I have been developing these horrible studying habits lately, I don't know what is happening to me. I used to study for hours and feel like I can absorb everything a professor will say in lecture, and now it's quite the opposite. My mind continues to wander, I find myself taking breaks all the time, and I just struggle to absorb the material a lot because I will have to refresh myself on the same information a lot. I don't have time for this and it's not helping me in the long run. Any advice would be nice at this point. I also have trouble sleeping.