werid redish discharge ??? almost like blood

I just had a weird redish discharge on my underwear and now am really concerned. I had my period and since than didn't have sex recently at all, I'm not on birth control, and i'mm just confused. Does anyone know what this could be from ? I am on Monicyclin (sorry if I spelled it wrong) it's a 100 mg pill from the Dermatologist, but I've been on it before so it's not that new. Also I'm supposed to get my period again in 4 days (that's what the cycle says) but it doesn't look like period blood too me ?