How do I increase my concentration?

I have been trying to study for weeks. Every time I open a textbook and try to read it, I can’t. I don’t know what comes over me, but it’s just impossible to focus. I have to read the same paragraph multiple times to remember what it said. I constantly struggle to understand the matter and have to keep re-reading the same lines over and over. When I sit down, I start thinking of something completely different and get up and do my chores. And I am sick to my stomach because of it. It’s like my brain is constantly distracting me from doing something important. I just wanna break it lol.