Apparently, as well as having antihistimine pills in your pouch, you should have self injecting adrenalin for future emergencies!
You should be able to buy this at a chemist in Thailand without prescription; or ask at the hospital.
I thoroughly recommend buying one before leaving Chiang Mai!
The site I looked at said, if problems arise:
Take an antihistamine (25-50 mg tablets or capsules of Benadryl by mouth) if you can swallow without difficulty.
If you are wheezing or having difficulty breathing, use a bronchodilator (borrow Geoff’s ventolin)
If a reaction of the entire body has been present, you should be given a prescription for a self-injecting epinephrine device when you leave the hospital. Inject yourself with a premeasured, prescription dose of epinephrine. Known as EpiPen or Ana-Kit (epinephrine), these self-administered medications are easily and rapidly injected into the thigh muscle. This is extremely effective and fast acting. Anyone who has experienced a prior anaphylactic reaction should carry these kits.

So there you are. I send this in an email but I’m not sure if you got it.