It is Blue Tansy that's recommended for reducing allergy inflammation in the aromatherapy literature. It's a very gentle oil, meaning it can be applied directly to the skin ~ one drop massaged each side of the nose...of course, it is blue, so will leave a little color while it absorbs. You might try using it in the steam as well. EO's in the neti pot need be EXTREMELY dilute...like, ONE drop in the entire wash (are you using enough sea salt in the water so it's not rough on the mucus membranes? I've found mostly that more is better
Another oil to give a try to is Cape Chamomile ~ like the Blue Tansy, the aroma is heavenly, yet it wont leave any 'blue' on you. While chamomile CAN be an allergen, this is a reaction to its dry, water-soluble components that should not be in the essential oil, and Cape Chamomile may be significantly different regardless.
Both may be worth sampling ~ the sample vials only have 10-20 drops, but should be enough to give you some idea of their affect for you.
Hope this helps!