Oh no, I had the SAME thing a few weeks ago! I spent too long in the sun and not only did my hair color fade to a hideous orange washed out color but my scalp was red and flaking! I washed my hair with a gentle shampoo with some mint in it to help cool and soothe my scalp, but also applied a sun protecting shield and aloe spray to it. I think you may be able to find some basic ones in your local drug type store,
Try a soothing UV protecting mist or mask as well which can help to hydrate the hair but also to soothe the scalp a bit. There isn't TOO much you can do but try to keep your head feeling comfortable with an updo, don't brush your hair too hard, and keep the hair hydrated with a hair repair serum. Andre Walker, Alterna and Josie Maran have some amazing sprays and serums to try!
Sounds painful and I hope it heals quickly. You may want to try Korres Yoghurt Cooling Gel.
I have seen numerous people try this product on their face and body and instantly their skin is less red and irritated. Because your sunburn is on your scalp I would recommend trying this at night and then rinsing it out in the morning.
Hope that helps.
I agree with Diana. The best thing you can do right now for it is to avoid the sun! I know how you feel it is sooo painful. In the meantime, try using a sulfate shampoo like the Carols Daughter Monoi Repairing Shampoo. It contains soothing oats and is extremely gentle on the scalp and hair.
Also, remember to keep your hair and scalp extra hydrated to prevent flaking and dryness.
Monoi Repairing Hair Mask