Hearing protection?

I would say it is likely caused by a combination of the heat, dust, pollens, noise, etc.

Easiest but most costly solution = Trade that machine in on a cab tractor with A/C.
If that is not an option do as most here have said and wear hearing protection and a good dust mask and drink plenty of fluids.

I'm right there with you as I made a huge mistake 8 years ago not upgrading to the cab on the machine I purchased. it would have been the best $5k-$6k I'd ever spent.
I was alright plowing and shredding on it but the absolute worst is rolling round bales. OMG

This is the most informative thread I have ever read here on the forum. I truly sympathize. I get a headache just riding around the ranch on my 4 wheeler. Hydration and an anti-inflammatory seem to be the only way to sidestep one for me. It really sucks. I learned some other causes I can relate to that might help keep me from suffering what is a common problem.

When I moved to the DFW area I discovered I am allergic to North Texas, (and when we go visit my folks my wife is allergic to South Texas), When I mow I always take a few precautions 1/2 hr beforehand I take a Claritin or Zyrtec, I wear a dust mask, and I hydrate constantly. I don't know about for your headache, but I also wear a hat and use copious amounts of sunscreen, reapplied often.

First time I blew my nose after bush hogging I knew I needed a mask. Used one the the blue surgical masks in a pinch last week and even it trapped a good amount of dirt. Started using ear plugs and I think that helped too. The biggest help I have found is one of those cooling towels that you soak in water, they work great.