Thank you for waiting. At age three, your hamster is quite elderly, and a car trip like that had to be quite stressful for him. I can give you some first aid measures to try, but an in person exam by a vet would be the best thing to do. Shaking often indicates dehydration and/or hypoglycemia.
Put a drop of maple syrup, Karo syrup, or honey in his mouth. Repeat this once per hour. Get some Pedialyte (made for human infants and available in discount stores and pharmacies). Use a syringe to put a drop at a time in the side of your hamster's mouth. Don't put it straight down his throat as that can lead to aspiration into the lungs. For the first hour, give some every ten minutes, after that, once per hour. You can also use a syringe to give him some baby food (with no onions in it). These measures may keep your hamster alive long enough to take him to a vet.
The lump in his ear may be an abscess or tumor that ruptured. It's not uncommon for these types of growths to rupture. You can put plain Neosporin on it twice per day. That won't make it shrink but can prevent infection in the open area.
You have apparently done a great job of taking care of him because a three-year-old hamster is the equivalent of a human well into their 80's. Because of your hamster's age, you'll have a decision to make. The lump could be due to cancer, an abscess, , or it could be a benign tumor. The only way to find out is to have a vet do a fine needle aspirate. When something like this happens to an older hamster, some people just let nature take its course and keep the hamster as comfortable as possible. Others want to treat if possible. If this is an abscess, it would be treatable. As hamsters get older, they do become more prone to some diseases that can't be treated. so, you'll have to decide how you want to approach this. If you decide on a vet, the following links will take you to directories of vets who treat small rodents. At the first site, you'll come to a log-in page. Sign in as 'member' and use 'member' as your password ***** well.
If you have more questions, just let me know. I hope the first aid measures will help your hamster feel better.
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