HELP! Question about the Pill.

How long does it take for your period to start once your pill packet is finished?. I had a normal period from 25th-29th of July. Then randomly had breakthrough bleeding which was really different from a normal period from 12th-16th of August (bright red/fresh blood). I say randomly because I have been taking the same pill for over a year. Then on the 27th of August I had a stomach bug which went away by the 31st and then had spotting for 2 days. I didn't take my pill the whole time I was sick and had the spotting. I had unprotected sex on the 3rd of September but took my pill that same evening. My pill packet ended on the 19th of September. Its the 21st now. Still waiting. Should I be concerned?