Is this a sunburn fever? Or from being sick?

Could be a combo of both. But if it isn’t going down, it probably has more to do with your illness. Go get it checked out. You may have something more serious than a bug. I’m sure heat exhaustion simply lowered your immune system and viruses are opportunistic little bastards.

Fever points to flu and not just a cold.

Usual response to flu is bed rest, lots of fluid, maybe some Tylenol to lower the fever and make you more comfortable.

Chicken soup or broth can be soothing.

You can have a high temperature with heat stroke/stress too. Were you not under cover? Do you have any other symptoms? Or it could be a result of you having the flu or a cold. I’m just getting over a bad cold that started with a terrible sore throat that made it hard to speak.

Take some paracetamol (which may be Tylenol under its brand name where you are) and keep your fluids up as @gailcalled has suggested. If you don’t improve you may need to see a doctor. If your temperature is very high, you should do that.

Take some fever reducing meds like Tylenol or Ibuprofen, keep yourself cool, light clothing, and even use cool compresses (damp cool washcloth) now and then. It doesn’t matter why, if you get your fever down you will feel more comfortable.