I Have Not Had But One Period In The Last

I have not had but one period in the last few years. Tho I was sexually assaulted this past Friday and still took plan B just in case because I recently was put on metformin which I'm sure you know can regulate the cycles. Anyway, I have no idea whether I will get a period or not, I just know that since taking it, I've had pink color when wiping but not enough to soak underwear. Just normal wipe. Should I be concerned or is this normal?     Should I expect a regular period or only what is happening already?