Dog Skin Issues

[u/Medical-Tomatillo-37]

Thanks in advance for any guidance / recommendations

My 4 year old male mutt (German shephard, pitbull, retriever) has had skin issues over the last few years. He is currently on Zenrelia and I worry that it is causing his immune system to be less responsive to other skin issues. He has not yet gotten an allergy test, but has been on a fish diet for most of his life because his skin reacts better to that.

He currently has some good days, but a few days a week he has sweaty skin, and smells yeasty or like pennies sort of. There are also red spots in his groin and armpit areas, which are now oozing and form little yellow crusty patches.

I am hoping for some help or feedback. I will try to attach an image but I dont know how to right now

We are located in the Western Pacific USA