My female SBT when younger use to have an itchy back side all the time. Her hair started slowly getting finer and would look like she was going bald but still had some hair there. I got a creme from the vet but it never worked. I found using bepanthen or baby powder worked for my girl on itchy or irritated areas. Good luck
Edited: She is now over 3 and has no problems with her skin, except sometimes from her collar (which she only has on when walking) under her neck it becomes red, I put the bepanthen on and it goes away few days after.