I had my period last wed till sunday, now a week later i'm noticing light and dark discharge spotting and gas trapped pain in buttt.am i ovulating????

Possibly: You don't usually spot or have breakthrough bleeding when you ovulate. It could simply be old, leftover blood from your period that is just now coming out, which isn't that unusual, although, yes, it is a pain. It sounds like it's been close to 14 days since you actually started your period, though, so you could, in fact be ovulating, I just wouldn't base it upon the bleeding.