Oracle, here's a link to a good article on ragweed allergies, with some treatment options:
http://www.theallergyauthority.com/a...agweedfall.asp
In particular, note the section on prescription nasal sprays (NOT the OTC ones, which may not be for allergies). It sounds like your migraines begin as sinus headaches from allergies and I can empathize-- I get the same thing a few times a year, though not from allergies. Migraines suck.