Implantation bleeding

[KJ268]

My girlfriend and I are not trying to conceieve. We are both 19 and have been together 3 years.

We always use condoms even though she has been on birth control for 5 years and we have both test negative for all STIs.

We've had maybe 2 to 3 instances where the condom came off and this happened most recently about 10 days ago. My girlfriend just finished her period the day before and when we had intercourse I did not finish inside her. She hasn't missed a pill in about 2 months and when she did miss that time, she was about 12 hours late and took it the next morning so she really actually late and didn't miss according to websites (It seems 24 hours is a miss).

Fast forward to this past Friday. She had random bleeding. It was like a light period, but wasn't spotting she said, she felt herself bleeding at times. It looked like a normal period to her in characteristics but just light. She said this has happened before to her. This lasted until yesterday so 3.5 days. She woke up this morning, tuesday, with no bleeding. As of today, she isn't due to have her period for 13 days, and her bleeding started with 17 days to go. I'm guessing with birth control, she is on a 28 day cycle since that's how many pills her pack contains (21 active, 7 placebo)

Could this be implantation bleeding? She wasn't really worried and had no other symptoms at all that usually come along wit implantation and 17 days seems too early for implantation bleeding. I read a week before your period is when but again I could be wrong. I know the only way to know is to test but when should see with the early response and do you think this is implantation bleeding?

Thank you

[KJ268]

bump

[KJ268]

I should add that the bleeding started about 6 to 7 days after sex and i heard that 10 days after is the earliest. So her bleeding for 3.5 days, 17 days before her period and 6-7 days after sex seems to make it unlikely that it was implantation bleeding but more advice would be greatly appreciated.