Thanks for that confirmation.
I'd find an urgent care clinic, make a call and ask them whatever details are necessary to have with you if you need to bring your boy in tonight. Since he's still producing atleast some urine/stool, is interested in eating/drinking and this is all rather a sudden onset, hopefully the cold packs will get his temp down and get you all through the night until you can see someone tomorrow.
This next advice is something I almost never recommend, but in this case and based on your own judgement, it may be worthwhile:
Aspirin for cats may be offered in certain situations, usually at a dose of 10 mg per kg (since 1 kg = 2.2 lbs, this is just 5 mg per lb of body weight). If you have a 6 lb cat, this would mean less than half of a baby aspirin (which is 80-81mg).
Between that and some cold packs (be sure not to use ice, or atleast wrap it very well so you don't hurt his skin with the cold), it should get the temp down and buy you some time until being able to get him seen first thing tomorrow.
With this said, do not hesitate to take him in if you sense even a little bit that it's necessary. You're seeing him and you know your cat - trust your instincts. Do not trust me and do not trust anyone or anywhere else on the internet ok? Only you are seeing him and know what you 'feel'.
Again, I'll be here for at least a couple more hours, so let me know.