Depo Shot

I am 18 years old and my period has been regular since I first started. I usually know down to the hour on when I should get it. I just got my first depo shot last month. This passed week I've been getting cramps, my head has been hurting, i've been nauseous, and I was due to get my period this morning. I know it's probably too soon to assume i'm not getting it, but has anyone missed a period while on the depo shot?? I haven't had any irregular spotting or anything unusual.