I've been toldvimhave oral thrush i'm in extreme pain and it look as though my tongue is splitting is this normal ?

Yes: Yes this can be a side effect of oral thrush. Try and see a doctor so they can prescribe you some antifungal medication.

Improve hygiene: Thrush occurs either from poor oral hygiene or low immunity. Begin gently brushing your tongue and cheeks regularly; at the same time see a physician to get an anti-fungal and rule out a systemic health problem. If you're healthy, then the most effective long-term treatment is to regularly disturb the environment in your mouth with a toothbrush by cleaning all the surfaces 2x daily.