I'd suggest starting with what the calculators say then applying some trial and error. If you gain on that number after a week - better two weeks, then decrease slowly, like 100-150 calories/day - again for two weeks at a time. If you lose, add 100-150 calories/day and see what happens.
eta: I read your profile and have zero experience with what you're going through. I think you should ask a doctor!
The side effects of allergy medications keep some people from using them. Natural remedies can be a great alternative, but some are more effective than others.