On The 1st My Girlfriend Took An Emergency Contraceptive Pill

On the 1st my girlfriend took an emergency contraceptive pill (Plan B), less than a week later (the 5th) she had her period. This would mark 15 days early to her usual menstruation. We had sex on the 5th day of what we believe is her normal period. We are both confused as to if this is her period or if this is "spotting", she says it's a little lighter than her normal period but we are concerned because it is so early that it may not be her true period. There was a small amount of ejaculate that got into her vagina but not very much at all. Is there any cause for concern for pregnancy?