Super confused!!

Maria

I stop breastfeeding my son 24/7 and I’m only doing it from 2 to 3 times a day suddenly I got my period June 23 and only lasted 4 day I had sex with my husband on the 26 now I’m 7 days late I took a bunch of pregnancy test and all of them came back negative can it be because I’m still breastfeeding my son??