Cat won't take antibiotics

Our cat has a bacterial sinus unfection. We first tried liquid Antibiotics and squirted them into his throat. He choked and gagged and got the liquid in his lungs so he couldn't breathe out of his mouth or nose for one night. That was too scary so we switched to pills. He hated getting the pills shoved down his throat so much that he developed severe anxiety and wouldn't come near us and refused ot eat. He lost 4 lbs. so we stopped the pills. Slowly he started eating again but he is still underweight. Now, 4 weeks later, the sinus infection is coming back. We are afraid to give him anything and right now are letting him coast, but what if he gets worse and possibly dies? Not sure what to do - any advice?

TIA.