Missed period, thick bleeding after missed period, two pregn

So about a month ago, my boyfriend was worried that he might have ejaculated in me and I never thought anything of it because I am on strong birth control, except I remembered that weekend that I hadn't taken my birth control for two nights prior to that happening. About two weeks ago, I missed my period. Then, about four days later, I started having wierd, irregular bleeding, kind of thick and dark. It's disgusting I know, but Im worried that's some kind of sign that Im pregnant. I had taken two pregnancy tests and they both said no before the bleeding started. Now Im worried I should go to a doctor and get a pregnancy test from them?

HELP! Any ideas or thoughts?!