D&c three weeks ago! Soo Confused help!

I had a d&c on Sept 19th 2014 due to the baby stopped growing at 8 weeks four days! Since I have been done bleeding (11 days after d&c) hubby and I have been having unprotected sex, I haven't felt good lately so I took a first response 6 day sooner test and got a postive. I then took one the next morning and line was darker! I called my docs office and she sent me for blood work my hcg level came back at -2 said I wasn't pregnant and all the hcg after the d&c left my body..I asked her why do I have two first response and 2 dollar store test that are postive? She said said did not no and make me a apt for Monday morning! Has anyone ever had this happen to them what's going on? I don't think I ovulated this month yet but usually I do by now! We're trying right away!