period 2 weeks late. one drop of blood the other day but no period

i had unprotected sex around the first week of July. I got my period about 2 weeks early around d july 18th. it was heavy the first day then extremely light the next and nothing the third day. i am now t2 weeks late with my period. i got a drop of blood the other night..literally one drop of blood! i thought i got my period but then nothing since then. That was 2 days ago. No cramping or any signs of a period. what is going on??? could i be pregnant even though i bled last month??