Terrified

I am 16 and march 20th I beleive cum might have gotten in between the lips of my you know what. It did not penetrate, but I heard just being in the general area could make me pregnant  today is May 1st btw and I didn't have my period at all in April but I now have brown spotting there's barely any in my underwear but when I wipe there is a lot. I took a pregnancy test two days ago and they were negative but I am so lost and terrified is it my period brown cause of old blood or is it implatation blood :(