I'm using something similar, I'm using "Fucidin H", which is a combination of fusidic acid (Fucidine) and hydrocortisone (low potency steroid).
Betamethasone (I think it depends on what kind of betamethasone it is, there seem to be different ones) is a (much) stronger steroid than hydrocortisone, so I personally would not want to use it first and without consultation of a doctor.
If I remember correctly, one patient had good success with Betamethasone, but another one actually got "full blown" EC after using it (he had minor lip problems before; not that that is proof it Betamethasone causing EC, but I would be careful).