acne + itch

I’m wondering if my english lab has sensitive skin or allergies! she’s had no issues up until the last month or so (she’s 2, but this is my first summer with her.) she’s got significant acne/bumps on her chin and had some on her reproductive area which are clearing up well. she’s also been scratching/itching herself frequently

what tests/investigation will a vet do if I bring her in? do you guys have food/supplement/OTC recommendations? (she’s currently on Purina Pro Plan complete essentials salmon)