I have a little bit of white stuff on the bak portion of my tongue, but how can i tell if that's just normal or if its thrush from my antibiotics?

Thrush: Typically when people have thrush they will complain of a whitish, cottage cheese like coating of their tongues. They often have a mild sore throat, and sometimes some difficulty swallowing. If it doesn't bother you, i wouldn't worry too much.

Tongue coating: Thrush is caused by an overgrowth of fungus. If you wipe it off, it leaves a raw, red surface. Build up of debris on the tongue might look the same, but you can brush it off and the tongue underneath is fine. Have your dentist take a look at it and give you a definitive answer.