I have a horse with allergies & hydralazine works well for her, pretty cheap too if you sign her up for a Walgreens health card.
Vaseline in her nose should help.
I've used the allergies shots 3 times. They have to be given according to a schedule for at least a year. Twice it worked & the things my horse was allergic to she no longer is. But those were food items, alfalfa & Johnson grass.
The shots didn't help my other horse with bug related allergies but the hydralazine does.