I Have Been Taking A Steroid For My Ulcerative Colitis,

I have been taking a steroid for my ulcerative colitis, and two days ago I haven't been able to pick it up. I am suppose to get my period in two days. Today I went to pee (there was no pain) and I noticed it was a dark red black (blood. Are there any STDs that would cause that as a symptom or could it possibly be a reaction to stopping the steroid/ something involving my period?