What is going on with my body?

My hubby and I bd on the 3rd of february and he d inside of me that night and a few more nights there after. We want to have another baby and decided to have another one now. I started having pains and slight cramping a few days after. Today I noticed some spotting that was pink and only a drop or two. I went to the br later and it had gotten darker and there was a little more of it. What could be wrong?