An allergy is an over-reaction of the immune system to a foreign protein through the release of histamine, which irritates nerve endings in the affected area, creating itchy and runny nose, water eyes, sneezing and so forth.
We have become accustomed to the variety of over-the-counter anti-histamine products to address the physical symptoms of allergies. But with those products come side-effects like nervousness, dizziness, sleeplessness, or drowsiness.
You have other choices if you wish to
avoid anti-histamine type 
products.
The first recommendation is to drink water. Dehydration can cause
histamine production as a process of the body's water management protocol.
So since the goal in relieving allergy symptoms is reducing histamine, make sure
your histamine levels aren't already elevated due to dehydration. For more
on how much you should drink, see the Staying
Hydrated tip.
Inhaling
a drop or two of specific essential oils is an aromatherapy approach to
allergies. Chamomile, melissa and eucalyptus are all proven allergy
fighters. Eucalyptus is a natural decongestant in addition to having
anti-bacterial and anti-viral properties. Chamomile and melissa (in low
concentrations) have calming effects on the mind and body. Since allergy
attacks tend to be stress related, these two essential oils in particular work
to calm the sympathetic nervous system which produces the "flight or
fight" response. If you don't have the essential oil of chamomile on
hand, try drinking some chamomile tea.
Homeopathic remedies include Allium Cepa, Arsen Alb and Euphrasia, in addition to the pre-packaged hay fever and allergy products. There are several brand name products available in health food stores. Follow the directions on the label.
Some dietary suggestions include reducing mucus producing foods like milk, cheese and ice cream. Vitamin C is a natural anti-histamine, so increase your daily intake to 2000 - 3000 mg. (If you begin to have diarrhea afterward, reduce the dosage.) Increasing you daily Vitamin A intake to 5000 IU's, seems to help some people as well.
You
might also try irrigating your sinus and nasal passages with a warm saline
rinse. This practice comes from the Yoga traditions. The irrigation
is accomplished with a neti pot, a small kettle that looks kind of like an
"Aladdin's lamp". It's very soothing to an irritated nose.
Following some or all of those suggestions will take care of the physical symptoms. The question still remains: why did the immune system over-react in the first place. No one knows why this happens. I would suggest a solution in the emotional and spiritual realms of healing.
Louise Hay in her book You Can Heal Your Life addresses the idea that physical symptoms represent some aspect of our beliefs, thoughts or emotions that manifest in our body. The solution is to identify the offending belief and change it.
For example, she says allergies relate to the denial of your own power. She would have you ask yourself: "who are you allergic to?" She suggests changing the thought pattern to "the world is safe and friendly. I am at peace with life."
Hay says sinus problems result from the feeling of irritation by someone in your life. The changed thought pattern would be "Peace and harmony dwell in and around me at all times."
It does make sense, after all humans are emotional beings. We sometimes lose ourselves in the big picture of living. As a comparison, how many animals in the wild do you see suffering from allergies? I would suggest that wild animals know their relation to everything around them and they never doubt it.
What is your relationship to the people in your life, to the things in your life, to your spirit? Are you living in harmony with who you really are, or are you denying some aspect of yourself? Therein may lie the ultimate cure to your allergies.
Sources
Batmanghelidj, M.D., F Your Body's Many Cries for Water
Davis, Patricia Aromatherapy an A-Z
Evans, Mark Natural Home Remedies
Gottlieb, Bill New Choices in Natural Healing