I got my 1st Depo shot on Dec 18. I had my last period on Dec 2nd-Dec 6th. I had unprotected sex on Dec 27. MycLadytimer app says that I'm suppose to get my next period on Dec 31. So the questions are: (1) How long does it take the shot to work? (2) is it possible that i can get pregnant because I didn't use protection? (3) When should i get my next shot? and (4) am i still going to gety next period on Dec 31 ?