I think i may have a sinus infection i currently take cyproheptadine for my seasonal allergies... will this same medication work for a sinus infection?

No: Cyproheptadine is an older and very sedating antihistamine. It is safe in pregnancy and is used to treat "cold induced" hives. There are many other (better) choices for allergies. That being said, it is very drying and could prolong your sinus infection. I would suggest you consider either doing nasal saline irrigations, add a mucous thinning agent, or take a decongestant instead.