Recurring skin sores on my six month old, any ideas?

[ChazzaG28]

does anyone know what this could be on my 6 month old?
at the beginning of June 3 red marks came up on his shoulder, then turned into the scabby/open marks you can see in the photos. The drs said it was impetigo, gave us antibiotics (a form of penicillin) and it went after the 5 day dose. 2 days after it was back again, so the dr gave us a longer dose of the antibiotics. It did the same, coming back on his nose, but the old ones have stayed on his shoulder but look circular with a whitish centre. The dr now says that could be fungal or maybe MRSA. We tried a different type of antibiotic but that was even less effective as before.
he is absolutely fine in himself, no temperature, feeding really well, lots of wet nappies. Just really want this to clear up, so any thoughts would be really appreciated.

Have you had allergy testing? My son started with rashes when he was a toddler, we had all the allergy testing and turns out he was allergic to our family dog!

Wondered about Ringworm ( fungal) with it being circular. Often very catching. I taught a child who had repeated infections and most of the class and staff got Ringworm too ( small class lots of staff, special school)
The source was the cat next door!
Hope you get some answers soon.

That looks sore. Maybe he needs a dermatology referral and someone to take samples to see what it is