Late period

Hey everyone! I recently had a miscarriage back in September (missed miscarriage) I had a D&C October 6th. I got a regular period November 5th. I was due for my period on the 3rd of December and am now 4 days late. I have taken 2 pregnancy tests that showed negative. I don't really know what is going on with my body at this point. My fiancé and I have been having unprotected sex ever since my doctor okayed it. Is there anyway I could be pregnant even with negative results? Please help! I am so frustrated at this point!