I am 19 years old, been taking birth control for the past year, sexually active, and took antibiotics February 7th through the 14th to treat a uti. Starting on February 11th, I have had light to moderate bleeding. Brownish red, and there appears to be tissue and blood like during menstruation. This evening I've been experiencing severe cramps, upper and lower abdominal pain, but tolerable after taking ibuprofen and use of a heating pad. Is this urgent? What's going on in my body?