I was on the depot shot for about 9 months and then I missed my last shot that I was supposed to get in mid September. Since then my boyfriend and I have been very careful not to have unprotected sex but it did happen once. I took an expired pregnancy test and it came out negative. A week or so later I took another pregnancy test that wasn't expired and it was positive but the second line was extremely faint. I have been having more frequent headaches and my breast are extremely tender. Is it possible to really be pregnant this quick after getting off the shot?