My boyfriend of one year and I had sex on the 3rd of December. My last period was on November 26.  We used a spermicidal condom and he never ejaculated in the condom. everything seemed to be right.  Him and I had sex again the 10th, but the next day I noticed a dark brown discharge. I disregarded it thinking it may have been our rough sex. The next morning I woke up with light blood that seemed pink. I am really worried that it could be implantation blood. I'm not sure if it could be from irritation or mid cycle bleeding. I'm confused because we did use protection and he never did ejaculate inside me. Any idea to what it could be?

**This is also our 4th and 5th time having sex ever and it's only ever been with each other