depo for a yr, feeling symptoms of pregnancy

I've been on the depo shot for 7 yrs off and on after my first child (7). I was on it again for a few shots and was unable to get the next one, then I had my younger son (5) there 18mths apart. Well like I said, I've been off and on the shot, I try not to stay on for over a year. Well I started back on it 6/10 and my last shot was 9/11, I haven't missed one. I've never had a period while on the shot. I've heard that it takes 2 weeks to "kick in" when you get the very first shot, but does that apply each time you get it? When I go to get my shots, I'm not given a test. Within the past few weeks I've been exausted! Sleepin at night and taking naps during the day. Right below my belly button is hard and my lower back hurts more than usual my hip started hurting this morning, I've had headaches, and I wake up with swollen hands and feet. I've gained weight everytime I get the shot even thought my diet has not changed, but its always been in my stomach that I've gained  weight. I'm very concerned about this and I'm wondering if I'm pregnant. With my 2nd child, I took tests for 3 mths before I got a positive. Soo... there ya go... any ideas? Ps... I will not be gettin my next shot,