can I be pregnant ?

Ok I had gotten my period last month on the 25 ok ? So ... I was suppose to get my period AGAIN ! On the 23 of this month but my calendar shows, that I am 4 days late .. I took two pregnancy tests today.. &&, shows negative, now my stomach feels weird and my boobs kinda hurt , every time I lay down on my side I get these pains, when I lay on the other it's the same even on my belly.. can I be pregnant?? I have been trying to convince for 3 years I just need to know.