Thanks for the query,
If it was staph a new lesion should not have appeared while on medication.
The diagnosis may be correct but probably the organism is resistant to the antibiotic you are taking.
Please get a culture sensitivity done.
This will help in giving exact treatment
Probably you are suffering from
Please meet a dermatologist
for exact treatment.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.