I had the depo shot for the first time at the end of June. Before that I have had very regular periods. Now that the depo has worn off around Aug 20 and I expected my period it has not come. I have read online that it can take time for everything to get back to normal as far as the period goes but I was wondering since it was only one shot and I am used to very regular periods whether that makes a difference as far as pregnancy likelihood right after the depo wears off. Plus I took an over the counter pregnancy test and it was negative yesterday. I am technically 3 week's late period-wise but don't know how serious I should take all that since I did have the depo. Any help is greatly appreciated.

The depo shot will seriously mess with your periods. Even one can take up to six months to wear off fully. Until your periods are regular again, you have to assume that you could be ovulating at any time, and take precautions.