I totally feel you, I'm heading back to college next week with BP2. I usually wait to tell my professors about BP until I'm more comfortable with them, usually I say things like "I have bipolar disorder and sometimes it will cause me to miss class or not fully participate or do poorly on tests. I just want to let you know, because it's important to me that you don't think I am lazy or that I don't care about your class. Sometimes I just have to prioritize my health over school, and sometimes my disorder causes me to mess up."
Also, I have horrible test anxiety, so I tell all my profs this and they have always been understanding, if I freak out in the middle of the test they will always let me leave the room and take a breather. I had one professor who even let me turn in my test when I was having an anxiety attack and come back and finish it the next day.
I also see a therapist through my school's counseling center. The cost is absorbed mostly by my tuition so each session is only $10. Seeing a therapist has helped me sooo much so if you are able to and aren't already seeing one, I recommend it
Good luck! I know you can do it!