Is it possible my migraines are triggered by pollen, allergies, or sinus pressure? i notice i get full blown migraines on high pollen days.

Yes: Headaches or some people call it loosely migraine if bad enough without proper diagnostic tools, can be triggered by humidity, time of day, and other conditions. Migraine is a more specific diagnosis for a vascular condition but like i said people call severe headaches migraine. If you can find out the trigger you can find the cure. See your doctor for advise.

Yes, yes and no: Pollen, yes. Allergies, yes. Sinus pressure, no. There's really no such thing as sinus "pressure." 99% of everyone who has "sinus" headaches really don't. "Sinus" is mostly a myth. It's a relic of the Dristan era of the 1960s when the makers of Dristan made a fortune with TV ads that made postnasal drip sound like the cause of all ills. It's a rare person who really does have "sinus" headaches.