could I be pregnant?? tell me I'm crazy


I had a MC on July 28, 4 days earlier my HCG was only 62. I didn't have a follow up hcg test to make sure it went down to zero. I bled heavy for 6 days. i started birth control (part of the IVF protocol) shortly after and I am now day 28 of my cycle, I had blood work yesterday because they saw what could have been residual tissue and my hcg was 327. I have been going though ivf so it's hard to imagine that we got pregnant on our own. I just doesn't make sense to me why residual tissue would raise my hcg that much higher and wouldn't I have developed an infection given the fact it's been weeks since I MC? help?