What Causes Spotting A Week After Sexual Intercourse?

I am wondering if I am pregnant. My husband and I have been trying to conceive for a few months now. I have been tracking my periods and ovulations on a calendar. My periods are regular and they occur within the same week each month. I last ovulated the week of February 23rd. And then the following week I have super light spotting that started brown and turned pink and a little red. It only lasted 4 days off and on and I wore a panty liner as needed. Implantation bleeding? My mom had it with her pregnancies. And then the following week when I should ve had a period I had nothing. I get nausea occasionally but nothing terrible. I also have been getting faint heartburn which is completely strange and abnormal for me. And I feel more tired than normal. I will test tomorrow morning but I am too curious to wait until then! What do you think?