cramps but no period?

Kd
On Thursday I had such crazy cramps I thought, "ok my period usually starts about an hour after this kind of crap happens" but it didn't. It is now Monday and I'm still cramping with period being three days late! Pregnancy test was (-) but I wonder if what I felt was implantation and I just tested before my body had enough time to build up the hormones. 
Somebody please talk to me about this. My husband and I have been ttc for two years.