I am hiv positive and started on arvs 2 weeks ago.

Proctitis: You probably have proctitis or, more seriously, proctocolitis. You might have inflammatory bowel disease, i.e. ulcerative colitis or Crohn's disease. These symptoms also could be rectal STDs, like gonorrhea, chlamydia (inclusing the serious chlamydia called lymphogranuloma verereum, or LGV), or herpes. Check back ASAP with your doctor, preferably the doctor/clinic treating your HIV. Good luck!