Is This a Chemical Pregnancy?

After many years of trying and a few losses, I received a positive home pregnancy test at 17 days past ovulation. However, the next few days afterward have all been negative with fmu. I should be 5 weeks pregnant and have a few of the symptoms of pregnancy, but not sure what to make of the negative tests. We are nervous about getting a blood test done and wondering if we should wait until the end of the week to give it enough time. Not sure what to do.