Stomach cramps/upset stomach & dizzy spells?

I've been off my period for a few days now and I've been having off and on stomach cramps and an upset stomach. I also randomly get dizzy spells and feel cold and clammy or I randomly feel like throwing up. I've been on depo since January of this year and I had a baby in Nov 2010. I got pregnant with him on the IUD so is it possible that depo isn't working and I could be pregnant again?!?! Someone please help! If I'm not pregnant than I don't know what's wrong with me.