I suffer allergies and I have a suggestion but it's not terribly vegan but it *is* a lot better than Allegra.
At the health food stores, they sell sublingual allergy meds. Sublingual means it goes under the tongue and they work wonders! I'm allergic to pollen, ragweed, dust, cats, mold... tons of stuff and believe me, they work. All you feel is great and the plus side is that there are no chemicle names in them, just "x-factors" showing the strength of the individual ingredients used.
The only thing non-vegan about these is that the inactive ingredient is lactose. I'm looking for vegan versions, but in meanwhile these are what I go to when things get bad.
The brand I use now is called Natra-Bio and the formula is Allergy (for some odd reason, the hay fever one doesn't seem as good). I've used these for years and they've knocked out everything with no trouble and no side effects. I don't even get sleepy or wired on these things; all I feel is better.
Give them a try.