Late Period. Negative Test. Light pink bleeding

I tried posting this earlier but i think it messed up. My gf and i had protected sex twice in the past month. Once on february 11 and once on march 4th. Both times we used protection. Her last period was February 4th. She has yet to get her period and has no real pregnancy symptoms. She started cramping on wednesday and today she had light pink blood spotting. She said when she put in her tampon there was darker pink on her applicator. We took 3 pregnancy tests and all of them were negative. We are not trying to get pregnant and our families are saying she is just starting her period but we really need some insight.