I would go to an allergist and be tested. I am allergic to horses, dogs, cats, weeds, mildew, dust, and the list goes on and on. You know, all things you can find around a barn. Allergy shots and an occasional dose of antihistamine and I am good to go, even though I'm around all those things every day. Horses aren't something they test you for unless you mention it though, so make sure if you go in for testing, you have them check it specifically. It also could have been a local plant giving you problems. The goldenrod around here always gave me terrible reactions this time of year. I have asthma triggered by allergies so it's nothing to play around with if they get severe.
"Keep a leg on each side and your mind in the middle"