I think Im pregnant?!?

I was given the Depo shot about 2 years ago and for the past year I have been trying to get pregnant but I have been told that the Depo could last for an indefinite amount of time, the doctor told me a year but Ive heard from other women that it was longer for them, normally when I am about to start my period my get sore and I have headaches and cramping, I want to eat everything, and I get pretty irritable, (its just how Ive always been, and yes I typically keep myself at home during the week so I don't have to subject anybody to my moodiness).....this month my 's are not sore no headaches no cramping except for and occasional sharp pain on my left side and no moodiness but I have had a very hard time sleeping at night and I wake up very early in the morning, I am 4 days late with my period and I want to wait to take a pregnancy test but I wanted advice from caring women who will be able to tell me what they think....am I pregnant? or am I late from being stressed lately? and could the Depo shot affect me for longer than the doctor told me ? please help