This sounds so familiar!!
Hi there, just reading this post and feeling for yah! Our girl Star is extremely itchy as well, and spends a lot of her day scratching, even to the point that she actually scratched one of her nipples off. :( She is a rescue, and when we first got her, we switched her food to Innova adult - I had great luck with another Boxer I had - but eventually, she got serious ear (yeast) infections. We took her to the vet, treated the infections, and switched her food to Innova EVO large bites. She was good for a few months, and then regressed with an ear infection. We treated the infection again, and then switched her food to Solid Gold Hund-n-Flocken (spelling?). We originally thought maybe she was allergic to the grain, but she still got the infections on the grain-free, so then we thought we'd try the lamb & rice combo. We took her off all chicken & turkey completely, and that has helped immensely. We were supplementing with The Missing Link but switched over to Solid Gold Seameal. She has been on this for 2 months now, and is doing very well. Her chewing on her feet has ceased - a HUGE improvement! Not only that, but they are not inflamed anymore. YAY!! She still scratches at her ears even though there is no infection, but we have a weekly regimen of cleaning them with the solution the vet gave us. It is getting better thought - she is not scratching nearly as much as she used to. We are very hopeful that this will continue to work, but if she regresses again (with the infections OR her scratching does not continue to decline), we may try either the Wellness CORE fish kibbles, or maybe raw. It's just a work in progress, and the main thing is that she is happy & healthy!
My best wishes to you - you might try the Solid Gold Hund-n-flocken or just go straight to raw. Good luck!!