What Causes Delayed Periods And Negative Pregnancy Test?

Hello, I am just wanting to know if you were able to give any advice on pregnancy. I recently had a miscarraige and had to have a d&c done,...I had a normal 28 day cycle first period. Husband and I started trying to conceive again,..i am 3 days late for my second period. I had some cramping 2 weeks ago on right side above pelvis,..and little spotting (which I was thinking at the time it was implantation bleeding). I already have a healthy 17mth old and fell pregnant with him straight away,..and second pregnancy which resulted in a m/c, i also conceieved first time. I have done 3 hpt,...and all say negative. Is it possible that I am pregnant or is my body trying to get back to normal?