Advice or opinions wanted!

My period is 4 days late. I am about to start a new birth control pack. Forgot to take a few days in the last pack. Of course had sex. Can't remember if it was the same day as the missed pills. Took a cheapie test and it came out negative. I have no symptoms for my period at all. Should I retest? Should I start a new birth control pack even though I don't have my period? I just don't know what to do. Someone help!