missed period, HELP!! pregnancy?

I need help.. so I started my period on the 6th of October, and ended on the 9th. On November 7th I had protected sex, the condom hadn't broke or anything.(btw i took a plan b pill the month prior) On the 9th-11th I went to a camp that was very emotional and stressful so that's what I'm thinking is causing my late period but here I am on the 21st still waiting for my period to start. My breasts feel very tender and bigger than usual and I've been getting cramps but I'm just really worried that I could be pregnant, idk. It's just a thought that I need some reassurance on..