What Causes Brown Vaginal Discharge And Bubble Feeling In Pelvic Area?

Okay, first, I had a somewhat thick, milky white (non-lumpy) discharge without any itching, burning or odor in my vaginal area, but my significant other told me it tasted "sour". 7 days after unprotected intercourse, I began having this somewhat thick, brownish discharge and it feels like I have a "bubble" in my pelvic/lower abdominal area. I've also been feeling a bit nauseous for the past few days, and I don't have acne but I've noticed a pimple or two on my face. I'm not on birth control, I've never been pregnant and I've never had any STDs. What am I experiencing? Confused.