What Causes Soreness In Mouth Along With Thick Coating On The Tongue?

My tongue has a thick film over the entire thing my whole mouth hurts I figured it was my bad tooth and the pain was bouncing around my mouth I just noticed a small strange brown mark on my lip inside I just finished brushing my teeth and my tounge is split down the middle and sore in three sections different lights and widths do I get it checked or just keep brushing?