Thanks for the query.
There might be an underlying infection at the bite site which is slowly growing.
Please get a culture and sensitivity test from the site done,
Based on this exact antibiotic treatment can be given.
Instead of hydrogen peroxide
you can use betadine
solution to wash the area.
Let me know if you have any other doubt.
Please meet a dermatologist
for exact diagnosis.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.