I'm a school teacher and I had PCP this october and as a result I was absent for 8 days, I also took an extra 12 days during the school year when i felt like I was getting sick,or to rest,Now I face the posibility of getting an unsatisfactory rating for the attendanve problems. Should I explain i have AIDS or just accept the unsatisfactory rating that could lead to other repercutions in my job ?

These are not your only choices.

Your other choice is to explain to your principal that you have a disability that is under treatment and you need a reasonable accommodation: you need an occasional day off when you feel as though you're getting sick to avoid getting truly sick. Back it up with a note from your physician. Your diagnosis should NOT be in the note or in the conversation. It's none of your employer's business. Employers deal with functional limitations and accommodations, not with diagnoses. They're not medical providers.

An unsatisfactory attendance record leading to a sub-par performance review is avoidable. Congratulations on recovering so well from PCP, by the way. Now you need to use the energy you've regained to establish a new relationship with your employer, one where you are being accommodated for your disability rather than punished for your occasional absence.