Allergy Help?

My dog is a mess and I know y'all aren't vets, but I am going to do this anyway.
Apollo (Great Dane) has always had pinkish skin and blood-shot eyes. Not too bad, but enough that people would ask me about it. He never itched or acted like anything was wrong. So, before I go in a million directions-

Symptoms: His skin is redder than it used to be. About 2 months ago or so, he woke me up in the middle of the night just frantic. He was whimpering, pacing, and scratching like mad. His eyes were the reddest they have ever been and his skin was bright pink. He is a harlequin, so where his fur is white you can see his skin clearly. On his belly and chest you can see it b/c his fur is so thin. Anyway, I called the ER vet and they said to give him 6 Benadryl. I did and it helped, but not a whole bunch. I bathed him- yes, at 2am, with allergen shampoo and put some Aveeno on him. That I think helped more than the Benadryl! So, he has had random outbursts like that off and on ever since. Maybe once or twice per week.

Food: The vet had me switch him to the "hypoallergenic" version of Eukanuba, which is prescription so it's very expensive. But this was at his check-up in JULY and he had no symptoms at the time. The vet put him on it b/c he has acne on his chin- always has. I did that food for about 8 weeks and he didn't seem any different so I quit and put him back on Nutro Natural Choice Large Breed formula. He has always eaten that and always seemed fine so I didn't see any need to up my pet food bill that much.

Environmental: In my gut, I think it is environmental. I just don't think its food allergies. From what I have red so far, some key symptoms lead me to say this. One is the part about sudden onset after the age of 18 months. He is 2 and a half. Also, his belly and feet are really red. The pads, and in between the pads, are blood red and he licks incessantly. No biting or hair pulling. Just licks his paws/belly and scratches his shoulder area with his back feet. Since environmental factors are normally dust and/or pollen, that is significant b/c they step and lay in it so those areas are very affected. On food allergies, no mention was made of paws being particularly affected or the sudden onset after a certain age.

Questions: Has anyone gone through this?! Should I have him allergy tested? Am I being too quick to rule out food allergy? I just don’t know where to go from here. I can't afford to go to the vet every other week for months on end and spending tons of money on "what if" scenarios. DH is in school for another year and a half and we are watching every penny. It's all I can do right now to get them all to the vet for regular shots- I have another dog and 3 cats too. Has anyone done allergy shots and did they work? I would just like a little "real person" info before I go to the vet. I would like to go in with a plan. Don't get me wrong; I will go to bat for this dog. We have already done the Parvo thing, and the expensive shoulder surgery because he's a genetic mess thing, etc. But that was when DH still worked full time and we weren't shelling out almost $3K per semester for college! Yikes! Oh, I switched him to Nature's Recipe Allergy formula, which is vegetarian. I am trying that as my own DIY "food study" to see if that does anything. However, I know a girl I used to work with fed her dog cooked hamburger meat and rice. That's all. She fed it for tummy issues though. Doesn't seem very nutrionally sound, but I though maybe for 6 weeks I could feed him that safely to truly rule out food allergies. I mean, if you do it right and don't allow ANY other food or treats, he only eats 2 ingredients so it makes that ruling out process much easier! Anyway, any and all help, suggestions and encouragement are welcome and appreciated.

Thanks-

Jamie and Apollo