As a long time sufferer from allergies, I spend much of my spring and summer avoiding all carbon based plant life and medicating in order to function. Needless to say this can take a serious toll upon my voice as most of the treatments for allergy symptoms cause as many problems as the allergies themselves. I take an allergy pill (Allegra), which reduces my symptoms but does not dry me out excessively. I must increase my water intake to combat the dryness as well as the heat and the resulting perspiration. I mostly remain indoors, but the air conditioning removes moisture from the air, which adds to my dryness. A humidifier can provide relief. I highly recommend that you consult a doctor to help you find the best medication for you and/or see if allergy shots might be an option. I highly recommend the latter!
KISS Rule - Stay hydrated in the summer especially if you take an antihistamine. Remember ... Pee Pale!