So.. 16 days late and I started spotting..

So today I started spotting. At my 5th day late i took a couple pregnancy test, the were faint positives. I have since gone to the doctor to have a pregnancy test done and it was negative. The lady said wait about 2 weeks then come back it just may just be to early to detect. I explain that I had already taken at home tests and they were positive. she said she couldn't explain why the results were different. So here we are at 16 days late and I'm just started spotting. I pray to god I'm not having a miscarriage. I have read about implantation bleeding. This may also be a cause, but not sure.. This waiting period is hard...