Shetland Stopped Eating Grass Hay

My 4 year old Shetland X Bean has stopped eating grass hay. Hes been off his food a bit for the last month or so, had him in to the vet a week ago to check his teeth. As suspected, he had retained a molar cap that was causing him discomfort. Vet pulled it, floated his teeth, and sent us home with Equioxx for a few days. His appetite improved some, but over the last week he’s decreased his grass consumption to almost nothing again
Bean has been on Bermuda grass for the two years Ive had him, along with a small amount of alfalfa for extra protein as he’s still growing. Through all of this, he has always eaten his alfalfa just fine. I will give him a Timothy pellet mash at times when hes been struggling with his teeth. He had quit eating that as well.
Vet had me take him off all grass today, alfalfa only until Thursday when he goes back in to see her. Had me start him on Sucralfate. Other than the eating, he seems normal. I have noticed him starting to chew on the wood posts in his pen and is resistant to grooming on his right side. Only new behaviors Ive noticed. Vet wants to pull blood and do a full exam. Would like some input from you guys on ideas on what this could be. Bean has always been healthy since I got him, a good eater, no issues.

Did you check his temperature?

I’d be looking for an infection in his mouth to start.

No temp, I’ve been checking it regularly since I noticed the appetite decrease.

Could it be ulcers? The resistance on his right side makes me think of that.

Ulcers all day. Having an empty stomach (from not eating because his tooth hurt) can cause ulcers. Pain and stress (also from his tooth hurting) can cause them as well.