I've always had really strong nails that grow long if I don't cut them. In hs, I used to write math equations on my fingernails in pencil. If I worried that the teacher was going to catch me, I could just rub it off with my finger. Funny thing is, I didn't really ever use them because writing them small to fit them on my nails helped me to memorize them!
I did okay in college chemistry, but that was 15 years ago. It's almost all gone now, although I can still recite most of the periodic table. Memorization is the key with most science and math courses, I've found.
queenb - does your school have a tutoring center? If your prof isn't helpful, maybe someone at the tutoring center would be. Unless things have changed, it's usually a free service.