Our Hector adopted us one day last August after he casually walked up to me as I was sitting outside my backyard enjoying the weather and talking on the phone. He was very skinny and had a scratch on his head (ear mites). We took him to the vet where he had b/w which was normal, got meds for ear mites and got all vaccinations.
The vet did mention to me that he thinks he might have a virus on his glands but said we could address it at a later time if necessary. Unfortunately I don't remember what was the name of the virus he mentioned. Fast forward to the last 2 weeks and I've noticed Hector is in pain when he eats. He is on both wet and dry food since I've been trying to get him to put on some weight (unsuccessfully, btw). As of today he is not even touching his dry food and only eats the wet food after I mush it up even more with some water. He is clearly hungry but is in pain when he tries to swallow.
I intend to call the vet tomorrow, but was curious to know if anyone can give me some ideas as to what it could be. He is our first pet and we adore him, he is such a great cat! Any ideas? I'm worried about my little guy. I am going to likely have to wait a couple of weeks until I can afford to take him to the vet, I'm worried this could be serious. As a first time furbaby Mom I'm still learning, any input is much appreciated.

TIA