4 days late, cramping and 2 BFNs

Hi...I get my period every 31days. I also get sore boobs two weeks before as well but it didn't happen this month. I'm currently 4 days late no sore boobs but mild cramping. It's very frustrating because I took 2 pregnancy tests that were negative (1 was a first response early result and the other a cheaper test). Could I be still be pregnant? Has anyone ever tested negative and then went on to get a positive? I miscarried last July also so I seriously need some hope...