I'm freaking out!!!

Ok I'm very admit about my birth control. But on the first I had a lose stool and had sex that night. I freaked out and took a plan b the next day thinking it wouldn't be effective and had a lose stool a hour after. About two weeks then. I've had a lose of appetite. Lower left back pain and like milky discharge. Could I be pregnant ? I've tested at the 14 days mark but my test came out negative. What could be going on with me?