splenda IS the devil. it messes me up really bad.
personally i'd rather just eat sugar- it doesn't make me sick and I know what it does to me- it just makes me fat if i eat too much.
introducing those chemicals into my body didn't agree with me and i honestly don't know what all those artificial sweeteners can do to me. i don't think science has had enough time to show whether they really are okay for us to ingest even. SO, for me, i'd rather just use the real stuff and watch my portions.
good luck, that has to be why your tummy is messed up.
PS My dad could not lose weight while using splenda. he cut it out and reintroduced real sugars and that's when the weight started to drop. I don't think that's a coincidence. Zero calorie sweeteners and low calorie sweeteners will trick your metabolism, it's a proven fact. It's better to just eat the real stuff in moderation.