Max's advice is spot on. There really does not seem to be a problem with pinning 1000 mcg eod for longer periods..I did not have any sides from it.
The main thing with the methyl B12 I have noticed is that the energy kicks in faster and is..well, "smoother" and more consistent for lack of a better term. I supposed because it is not rate limited by conversion.
For allergies, use the aforementioned protocol and throw in some magnesium. According to my alt medicine texts, magnesium plays a role in immune system modulation and in real life it does seem to help. In any case practically everyone is deficient in it so it can't hurt. Solaray has a Magnesium-Potassium Asporotate with Bromelain that is very nice for this purpose. Bromelain has great anitinflammatory properties and helps prevent cancer.
If these measures don't bring 100% releif, try adding in several doses of Quercitin-Bromelain-Vitamin C per day. I've had pretty good luck with QBC and it should be available at most health stores. Ester-C is another great add in.
Keep your fish oil doses somewhat high and consistent.
If THESE measures fail, lemme know and we can start an allergy thread and list out the whole array of supps out there...either that or go on meds because you are an inflammatory nightmare.