bleeding while on birth control

Okay so Iv been on birth control for about a year and 4 months now and I am in a sexually active relationship. I missed 3 days of the pill because I was on a cruise and I ran out and when I did have sex he never came in me. But Iv been having some cramps and headaches lately and today when I go to the bathroom I find that I have a little bit of blood on the toilet paper and I don't know why. ( I have already caught up on the rest of my pills as today is already Wednesday of the following week. Could this be implantation bleeding? I also took my sugar pills one week in advance so I would have my period in the cruise so maybe this is my body being used to getting my period at this time. Can anyone assume or guess or kinda what's going on? I'm really scared and I'm taking a pregnancy test soon just in case.