help!!!

so about 3 months ago me and DH had a missed miscarriage. I last had AF on Aug 10th, and we did the deed around ovulation. AF was due yesterday on the 12th and today the 13th, I felt kinda nauseous in the morning, so I decided to test. I got a faint positive! but when I took 3 more, they were negative??? I'm so devastated and confused. Did i get a false positive or is my pee too diluted with water to catch it now? I'm testing again tomorrow morning first thing in the morning. If I am pregnant I'll be 4 weeks and 3 days. So it might be just too early? I don't know how to feel right now. Has any other ladies had a positive first and several negatives later and still been pregnant? please help!!!