It seems that you may be having insect bite.
There is painful swelling with erythema with soreness.
Your descriptions clinch towards insect bite induced dermatitis
Thorough examination is needed for the diagnosis.
For that , you consult dermatologist
Antibiotics , steroids and anti inflammatory drugs may improve the condition.Local antibiotic
may be needed.
Elevation of leg may be helpful.
Wash with dettol antiseptic is neccessary to prevent further spread of infection.
You may be benefitted.
I hope you got my answer.
Dr. Ilyas Patel MD