plan b and my period ?

Long story short, I was on antibiotics for 10 days. Pharmacist said to use back up method of bc, but I had sex once unprotected. I took Plan b along with my bc even though I read a lot that antibiotics do not affect your bc. 
I was supposed to get my period yesterday but it never came until the night, I think ? I'm bleeding a tiny bit but it's not even blood ? It's like pinkish discharge like what would be there before my period & after. It's not heaving at all like my normal periods and it's worrying me. Is this normal after taking a plan b & do I count this as a period?