Help :(

On the 23rd of July I had unprotected sex. On August 1st I saw light pink blood and the dark brown a little bit later. I missed my period. And my nipple are insanely sore and I feel like vomiting for the past 2 days. I took 3 preg tests from the drug store and they were negative. It could be possible I'm pregnant but the tests keep showin Negative. What should I do?