Nonstop itching feeling defeated

Here is a little back story, I have 4 year old Saint Bernard named Cheeba, and a 3 year chihuahua named nacho. For the last 2 years we have been dealing with non-stop itching. My dogs are completely miserable, they are depressed. When it started 2 years ago, it was winter and it was almost instant, they were itching til their hair was falling out and bleeding. I thought it might have been because of the dry weather. Took them to the vet, he checked them for allergies, mites, fleas, said their skin doesn't seem dry, he gave us a shampoo and sent us on our way. The itching continued, (while using and trying literally every item you can buy from vitamins and shampoos to sprays to anxiety vests and everything in between. Non stop vet visits and prescriptions. With no luck. Fast forward to this February 2017, my Saint Bernard gets hot spots for the first time from itching, so infected so smelly, she had to be put under and have them treated. Doctor gave her special bath stuff, spray, steroids and antibiotic. And the itching continued. After another mite, flea, allergy check and multiple vet visits, we are still where we started. My dogs have lost all life they had in their eyes. We have treated (and completely remodeled our home), I treat the back yard once a month. I buy them new bedding every month, they are on a plain chicken diet. They take probiotics, they are bathed, vaccinated everything. I am out of options and so defeated, my heart is broken for my dogs, they are healthy as can be, except this itching. I feel like our vet doesn't care. Has anyone dealt with anything like this ? Any ideas what else I could possibly do? They are very loved and cared for. We want them to get better so bad. Please help!

Have you tried varying their diet?

Just a thought, but my girl is highly allergic to chicken. Try a novel protein. Salmon and potato is good. This way you have ruled out all previously given protein and also cut out any gluten.

If you see an improvement, wait until they are clear then introduce one food at a time for at least a month to see if the symptoms come back. It's a way to gauge what they can and can't tolerate and if nothing changes, at least you can more or less rule out food as the cause

Have you considered feeding a raw diet ?
This choice of feeding is proving to be very effective against persistent itches and allergies, with better health in general.
It is easy to feed, there need not be any blood or smell, and our dogs stomachs are designed for this product, their teeth too!
Continuous shampooing can remove natural oils in the coat and on the skin, causing dryness and itchy skin too.

I've experienced something similar with one of my dogs, the first thing I would suggest as an idea is, treat the immune system. Feed a high quality grain free food(s), initially anyway cut out treats, and add maybe sweet potato or butternut squash as a filler...I'm sure there are plenty of other options too. Try treating the topical hot spots or rash areas with chlorahexidine... there's a spray mousse you can get, I think you apply it once a day.. dogs seem to quite like the application, at least that is my experience. That worked for me, it wasn't an overnight fix and it didn't completely get rid of the condition, but we certainly got right on top of it.
Regards

My dog had a similar problem, spent lots of money at the vet with no results. One day they decided to put him on comfortis which is a flea medication. We were already giving him flea treatments and the vet could find no fleas, but once we put him on this comfortis all itching went away. He healed and hasn't started again.

Have you had their hormone levels checked? Also have you tried a antihistamine to help stop the itch scratch cyle?