One combination I swear by is peppermint, lavender, and lemon in either a rollerball or diffuser. It’s saved me so many times and, as a bonus, it smells pretty good! I had mentioned this to someone in a Discord server I’m in, too. They don’t have essential oils so they instead used strong infusions of peppermint in some hot water with lemon juice and are having good results, too. Allergies suck so bad 
I know how you feel!
There’s even a sinus clearing recipe here somewhere…here, I found a few links you might try!