Copper’s personality has completely changed

Hello!

Copper’s problem is a complete mystery to me and there are so many variables so I’m going to try to keep this short and tell everything in chronological order.

Copper is a handsome male Himalayan kitten. We have had him for about 2 months now. When we took him home at 3 months old, he was incredibly playful, active, and fun. We have 3 other cats and are familiar with regular kitten levels of playfulness, and Copper was more energetic than any of our other cats at his age. Our other cats are 3 adult males. 2 twin Persian mixes around 14 years old, and a 2 year old Egyptian Mao. I was very careful when introducing him to the other cats but failed to help them become friends. Their interactions are always supervised, but the closest they’ve ever come to contact was sleeping on the same bed together. The older boys have swatted at Copper a couple of times. Our 2 year old cat was the only one to play with Copper. They’d play tag and hide and seek for a few weeks until our older cat got too fast/aggressive and it started to scare Copper. Copper had worms (he’s since made a full recovery) and was literally pooping himself in his sleep, and in spite of that, he continued to be fun and playful to the point where he wouldn’t let me sleep. About 3/4 weeks ago, I noticed that all he did was sleep on one chair, never demand attention, and never ask to leave the room. Whenever I take him outside, he usually wants to go right back inside, or he waits a few minutes at the most. He doesn’t play at all anymore. He used to play with patterns on the floor, lights on the walls, stationary balls, and just about anything he could reach. He still eats and drinks well and his stool and urine are fine. The only other issue is that we noticed he scratches A LOT. His skin twitches and he seems incredibly irritated, frantically licking and scratching at himself and it never seems to comfort him. The vet says his skin is fine and he’s just trying to scratch his ears since it turns out that he has ear mites which he is currently being treated for. I don’t think the vet is right about him trying to scratch his ears. Something is very clearly irritating him on his body and I can’t see what it is. His skin is perfectly clear and a healthy color. The only other factor is the single vaccination he took on the 25th of November which I am also suspicious of. He hasn’t been vaccinated since since he had a minor cold.

In summary, the factors that I think may be causing the major shift in his behavior are:
1. That he got so scared of the other cats that he’s lost interest in play. (He’s always been supervised and they’ve never hurt him though he is scared of them.)
2. The vaccine which, according to the label, is for “Feline Rhinotracheitis-Calici-Panleukopenia”. One of the listed side effects is temporarily sore joints but perhaps this has lasted longer for him for some reason. I can’t pinpoint the exact time his behavior changed but it is in the general time period in which he was vaccinated.
3. Whatever is causing his skin to twitch and the constant scratching.
4. Ear mites. (Why would that cause lower energy levels/activity though?)

I’m just theorizing at this point. My vet hasn’t taken my concerns seriously and has no theories on the lack of activity. I also am not convinced by his explanation of the itchiness as being attempts at scratching his ears because of ear mites. Vets where I live aren’t the most reliable and he very well may have messed up cleaning his ears and damaged something that helps him keep his balance which is causing his inactivity, or the vaccine was administered incorrectly somehow and has harmed Copper. I have no reason to believe either of these things other than that there is no explanation.

I have no idea what to do or how to help Copper and if anybody has had a similar experience or any ideas of what I can try or do to help him, Copper and I would appreciate it endlessly. Thank you so much for reading all this and for your help!