Swollen Glands or Lymph Node

One of my six month old bottle babies has a swelling on the left side of his neck. He was neutered, vaccinated, and got a microchip on oct 3 2015.
The node is about the size of a grape and situated beneat his ear and jawbone. I don't feel any other swollen glands or nodes anywhere else.

He's started to get very lethargic as of today and last night and I noticed his inner eyelids are slightly closed and he has a bit of clear fluid draining from his eyes. I took his temperature, despite his wiggling, and it read at 103.5° F, which is a tad higher than I'd like it.
He's not been sneezing or coughing, but I need to check if he's still the crazy food hog he was yesterday.

I'm really worried. One of my young female mice died yesterday of pneumonia, possibly brought on by mycoplasma.

I've always tried to abide by basic quarantine with all newly aquired animals, but it's entirely possible that a bug slipped through. I have very little money, and about eighty percent of what I get goes directly to animal care.

Has anyone experience this before and what was the result? He needs to go to the vet, of course, which I will get him to as soon as I can, but I am super nervous.

Now his temp is closer to 104.

I agree with you that he needs to see a vet ASAP. I don't know about the mouse connection, but he is clearly sick with something.

The vet prescribed Clavamox at the standard dose (62.5). Hopefully we'll see improvement in the next few days.

I would look up some natural home remedies or products for vaccination reactions. Look up anti-inflammatory remedies/products, specifically. There's a liquid vitamin C formula called Vita-Cat that I've used and seems to work well. It concerns me that your vet would neuter, vaccinate and microchip him all in the same day, especially at such a young age. Our vet spreads out the vaccinations for our kittens with at least 2 weeks in between each shot and always allows a few more weeks before being neutered/spayed. I would think that this is probably a result of his poor little body being overwhelmed. Have you used this vet before? Give him lots of love and as much nutrition as possible. I'll say a little prayer for him. 

He was sterilized at a spay/neuter van. Because I rescue so many cats, I don't have the funds for doing a neuter through the veterinary office. I agree that it is a little much to be done on the same day, but being neutered is better than being intact. His neuter was about three months ago now, though a reaction to the vaccine, despite nobivac's reputation, is possible.

His temperature has gone down now, to about 102.8° F. He's still lethargic, but it hasn't gotten worse and he still enjoys attention. His sister had a fever a couple weeks ago because she was teething, but there was no noticeable swelling. Hopefully if he has an infected teething problem, the clavamox will clear it up. Dental problems can be a pain.

I'm happy to say that he is still eating, but with a bit less... gusto than before. Still, three small canned food meals a day with electrolytes mixed in and a quiet space away from the other piggies at least while eating is a start.

I'll definitely look into the vit C supplement, I've been trying to find something good for a while

Anyway, I'll continue to update on how he's doing for the benefit of others who may face similar problems in the future.