I had terrible hayfever while preg (as always sigh) and the stupid pharmacist gave me antihistamines, which I found out AFTER TAKING THEM, you're not meant to have. *anger* A neti pot/other form of nasal irrigation is the best, I have a neti pot myself.

It's best to avoid medication while preg as much as is humanly possible, just in case. I took fenugreek to increase my milk supply after preg and I found that helped my sinuses as well. You'd have to find out whether that's okay to take but I imagine it is.