Am i not pregnant? I need help!?

so i had unprotected sex may 7 and may 10 and iget my period every 23rd ,, which is a regular period. And i went to planned parenthood and they said it was a negative result, and i get my period regular! So when i got back 4rm the clinic ihad brown spotting with a little blood, and ihave cramps! And usally when i get my period nothing but blood comes out, no brown spots or anything. I get borwn spotting only when im gonna end my period. Im confusedd?