TTC, multiple negative HPTs, AF 2 weeks late

My husband and I started TTC last month on my ovulation day (July 3rd). I immediately felt nauseous, cramps and back pain. I'm still having cramps and back pain but no AF (which was due July 17). I made an OB appt and did a urine test there, which was negative. The OB gave me a pap smear and pelvic exam, which both were fine. She did say my uterus felt enlarged like I am in fact pregnant. She also kept making comments like she believed I was preg. My cycles are very regular and I have never taken any BC. She said I'm lucky bc not many people get pregnant on the first try. Then told me to come back for a HCG blood test in a week (which will be tomorrow). She said if the blood test is negative then we will have to figure out what is going on with me and why I missed my period. Has anyone had multiple negative HPTs but still were pregnant? I also spotted dark brown blood for 3 days a week before my period which I have NEVER ever spotted. Not knowing is the worst!