Pain Killers make stomach pain worse???

I have recently experimented with pain killers (both Vicodin and Tyonel w/ Codeine) and have found that both times I have taken them they have made my stomach pains much much worse. In fact, when I took the Tyonel w/ Codeine, my stomach pain got so bad that I almost had to go to the ER. Has anyone ever heard of this before? Also, does anyone have any ideas at all why this may be happening?

Any advice appreciated.

Thanks,