Should I take the morning after pill?

My boyfriend and I had unprotected sex and I am on my period and the combination pill. I usually take the pill within 3 hours every day however one time I took it about 6 hours late. He pulled out and I went into the shower to wash everything off. I am certain that some of the cum got into my vagina as I was showering. I am worried and am not sure if I should take plan B. Again I am on my period and have had a regular month of combination pill although December I skipped a few doses. Please if you can help let me know.