CD38.. help!

Im 29, no birth control since my IUD was out over a year ago. My periods are regular.. 4 days of bleeding and 28-32 day cycle and I'm at 38 days now. I've taken 2 first response tests and they both are negative. We have not been trying and just withdraw. I would love to be pregnant, but what is really going on?? Im not stressed.. no major weight loss, gain, changes, etc. Ovulation wouldve been around 12/22-12/24 and we had sex a few time that week. Could I still be pregnant with the negative tests?