Could alcohol be triggering my sinus allergies?

Yes. Alcohol causes nasal congestion by a different mechanism than an allergic one. Perhaps that's a good thing; I've yet to meet someone truly allergic to alcohol. Unfortunately it means that allergy & alcohol ingestion work together to make your stuffy nose & sinuses even worse than ether one alone. You probably won't get much enjoyment from alcohol when sinus or nasal allergies are acting up.
Probably not. But alcohol itself can produce the same symptoms - stuffy, runny nose, from directly releasing histamine. In addition, alcohol increases the chance of chronic infection, which worsens all of your symptoms. If you are talking social drinking (1-2 drinks once or twice a week), it probably is not a factor. But heavier and more regular drinking is not good for your sinuses, or for you>.