I've My Last Period Was March 8- 15, I Haven't

I've my last period was March 8- 15, I haven't had one yet it's may 13, in April I don't remember when but after intercourse I saw three drops of blood but haven't seen any since until tonight I went to pee and I wiped I saw a very small blood clot but no blood in the water or on the tissue when I wiped again my period hasn't always been on time but never ever two months late, I took a pregnancy test like 2 weeks ago but it was negative... what do u think?