Old blood or something else?

I usually get my period around the 9th/10th but in March I got it the 29th-2nd I thought it came early it was dark but my flow was really light like I’m on birth control I have been since July 2017 but my last pack I missed like 3 days but me and my boyfriend used protection so last Friday the 13th I started to bleeding again and it was super light and a pinkish brown color and it’s been a week later I thought it was over I didn’t see any more on my pad so me and my boyfriend had sex and when we were done he said “I think you’re bleeding” and it’s the tiniest amount of brown I’ve never had this before and it’s still like that after 3 days I didn’t know if it could be old blood our hot water isn’t working also so I’ve only been able to wipe off with baby wipes and not properly been able to take a shower so I didn’t know if it could be old blood or some kind of infection I’m not cramping no pain down there it’s not burning or itching I feel fine just a little worried