Hi welcome to Health care magic forum. An insect bite wont stay so long. i advise you to consult a doctor for diagnosis and treatment.
You may need to get biopsy
of the lesion besides other routine tests for confermation.
Besides i advise you some diet recomendations as Avoid taking brinjal and sea foods. take more of green leafy vegetables pulses sprouts
egg meat milk fruits and juices to improve resistance blood and general health.
Wishing for a quick recovery and thanks for calling.