I was on the depo birthcontrol shot but have been off it for 2 months now an I have had unprotced sex a few times an now I've been having bad back pain an headaces an heartburn an my stomach down by my ovaries hurts I'm not sure if I have missed my period or not because the depo birthcontrol shot made them irregular, could I be pregnant?

Yes, sine you don't know when the period is, will be an issue testing, so you can test every week or two for about a month and see if it shows up.
Test with first urine of the morning.