Have you tried changing his food?
We had the same thing in the Uk and it did seem to make him worse, cortisone creams, he was ALL weeping skin. We thought maybe he was allergic to milk, which ran in the family, but doctors said no and gave him all sorts of antibiotics etc, horrible stuff designed by idiots who never tried getting it IN a baby.
Then after months of tests my MIL visi8ted, took 1 look and said' he IS allergic to milk'- he was breastfeeding and I don't drink much milk so we were sceptical but tried it. Anything to stop having to practically tie him up and stop him waking covered in blood from scratching his face on his sheets. And it helped.
When we were in NZ I eventually stopped breastfeeding, as whatever I tried to cut out eating wasn't working, and put him on a special cow-milk- free formula (which we can't get in HK) and he is MUCH better. The annoying thing is, from 6 months on nearly every parent seeing his wee red patches (flare up now & then when he tries a new food that has milk in it we didn't notice) said' is he allergic to cow milk'. LOADS of babies have it.
Now he's 11 months we are using goats milk powder as we try to wean him, can get it in some supermarkets - its not formula but he eats/ drinks other stuff so is OK.
Also I found Bepanthen very good - the nappy rash cream? I put that on every few hours when he has a patch, with the cortisone 1x day as prescribed to keep infection down. Hes almost OK most of the time now...
good luck!