two weeks late

Ai
This is my second cycle after a D&C in September. I had a tiny bit of what I thought was implantation bleeding about 7 days after o. I've had a sore lower back, sensitive breasts, some cramping on my right side. All pointing to pregnancy, yes? 
Well I finally got up the guts to tell DH my period was late and I've tested twice. Each time clear negatives. What could be going on? At this point my cycle is longer than after my D&C and after coming off birth control.  
If it was an early missed miscarriage wouldn't I still have a positive HCG
I'm going to go to the doctor on Tuesday but I'm just so perplexed. And I can't help wondering that something terrible might be wrong with me.