Brain fog is the worst. I have it very often.
Making tons of notes is useful. Notes, to-do lists, alarms - whatever you need to make sure things get done. Keeping a notebook with your lists and reminders would be helpful… if you remember to check it.
When I'm in the process of doing something, I find that taking frequent, short breaks helps me stay focused. If I notice I'm losing my concentration, I'll switch to another task for a bit, then switch back. At work, I keep a drink in the break room and anytime I start losing track of what I'm doing or getting overwhelmed, I just run back and take a drink. The small distraction usually sets me back on track. When I worked as a paralegal, I would just give myself a short break of a different kind - occasionally allowing myself five minutes on the forum or Facebook, stepping outside, or getting a snack all helped.
Like NGNG, I find fresh air and certain beverages to be useful. Caffeine can keep me on track, but if it bothers your stomach it's not worth it!
Also, when studying, try to treat yourself every once in a while. Finish reading a chapter? Awesome, you get a snack. Finish writing a page of a report? Great, step outside for a minute. This will break things up so you don't feel as if you have to concentrate for such a long time. It still takes longer than it otherwise would, but as long as you can get it done, you're making progress! It's still more effective than completely spacing out all the time!
The disability services at your school can be a help even if they are a hassle to deal with. At the very least, e-mail your professors and tell them what's going on. Provide a doctor's note directly to them if necessary to gain yourself a little leniency and understanding.
:hug: I hope things get better for you!