My last period was Jan 20 and on Feb 1st I had unprotected sex, but we used the withdrawal method. On the 3rd and 4th, I had some brown spotting. On the 10th I had some pinkish spotting with a little bit of red, but no clots. This is fairly unusual for me but I only had this spotting once when wiping. Everything I read online said that implantation bleeding lasts a few days. Is that true and should I just dismiss it as some mid-cycle spotting? What else could be causing this spotting?