Im sorry to hear about your DS. I dont have any advice but i hope some one can assist you.

DD went thru phases where she wouldnt drink either. I tried new bottles, new teats, different temp for her milk. I got best results changing teats though.

I guess if he isnt drinking milk, u need to make sure he is getting fluids other ways then. Water in a bottle, sucking on wet face washes, ice cubes, warm water.

HTH