Talk to your doctor and consider going to an allergist. They can help you develop a better plan for your specific allergy, which may include shots or some other treatment to lessen the allergy over time. It may also be possible your allergic to hay or something else in the barn environment and not actually horses, so an allergist can help you pinpoint what you're actually allergic to.
The antihistamines don't seem to work* they make me dopey and sleepy even the non drowsy ones. Any suggestions. Giving up horses is not an option 😂 at the moment I wear a full face mask and it helps too but I find it makes be a bit dopey too