I know you asked for natural remedies, but since you mentioned that you have tried oral antihistamines, I thought I would address another option. Oral antihistamines work fine for nasal symptoms, such as runny nose, sneezing, and nasal congestion. However, they do little for the itchy, red, watering eyes that you get with allergies.

There is a newer medication, (it's been available as a prescription for a few years) that is specifically for eye allergies and is now available over-the-counter. It is called Zaditor (Ketotifen fumarate ophthalmic solution). These drops are different from the typical vasoconstrictor ("gets the red out") drops. Zaditor actually inhibits mast cell production (the allergy cells that cause all the symptoms) and is also an antihistamine. It does not have a vasoconstrictor.

I find Zaditor drops to be very effective. The prescription strength is what I have used, but it is now available over-the-counter in the same strength.

So, try the saline eye drop washes, use a HEPA approved air cleaner in your bedroom at night, and dust your house (esp. the bedroom) frequently. If you still have symptoms that bother you, try these eye drops. Hopefully, they are also available in generic (cheaper) form.

Hello there, @kerryk!
http://dingo.care2.com/greenliving/rose-water.jpg
Everyone wants a clear and healthy vision but sometimes, allergens would get in and cause trouble for the eyes thus making it red, watery, itchy, painful and blurry. But worry no more because Kevin Pederson (Home Remedies) shares very helpful home and herbal remedies for your problem. So here are his suggestions:

1. Apply rose water to both eyes. After applying, shut your eyes off for five minutes in order to soak the eyes and allow the rose water to heal it. This remedy has been said to be proven effective and been passed on from generations to generations.

2. Consume 1 tablespoon of Indian gooseberries powder and honey mixture. This is the one you need @kerryk in order to develop immunity against allergy. With this said permanent relief, you'd be able to see the difference in just a couple of weeks.

3. Take a homeopathy powder called Merc cor 1M once a month and see the difference in just three doses.

4. Aside from remedies, you also need to take necessary precautions like cleaning and making your eyes free from dirt and dusts. When going out, always wear sunglasses. If your eyes feel itchy, avoid rubbing it with your fingers to prevent it from being more irritated. Splash cold water into your eyes and avoid using contact lenses. Avoid watching TV and using computer for 15-20 minutes in order to rest your eyes. Take enough iron, calcium, mineral and protein. One fruit that I have learned to be good for the eyes are the bananas because potassium keeps it moisturized.

I also suggest a saline eye solution. This works to relieve allergy symptoms by "cleaning" out the allergens. Another possibility is to a drop of Eucalyptus essential oil under the nose (perhaps diluted with jojoba or another carrier oil). This may help to calm eye allergies just like it calms nose allergies.

Some eye drops that offer relief for allergy sufferers tend to dry out the eye. Have you tried using simple saline eye solutions? This helps to cleanse the eye of allergens and yet doesn't dry out the eye.
Here are some other tips that might help eliminate some of your eye irritation problems.
For outdoor activities try to find a pair of sunglasses that wrap around your eyes, I read that this can help block some airborne allergens from contacting your eyes.
For indoors, try to keep your home free of allergen inducers such as placing throw pillows in the dryer on FLUFF/ AIR for 30 minutes on a regular basis. If you have drapes or curtains try to launder them regularly if possible. A lot of people leave small blankets tossed over the back of sofas and chairs year round... these need to be laundered regularly or at least tossed in the dryer to rid them of dust and other airborne allergens. Rugs should be vacuumed often (while wearing an allergen mask or bandanna over mouth & nose). By a good allergy filter for your home heating & cooling unit also. If you live in an older house you can also buy cheese cloth and cut it to fit the air vents in your wall or ceiling, place it on the inside help filter out dust and other particles.