Read and understood your history of an insect bite that has caused significant bruise.
You can do either of the things whichever can be done at the earliest as you may need the proper medicines like antibiotic, anti-inflammatory particularly the steroids and antihistamines as soon as possible to avoid the spread of the poison and/or infection.
Till then just apply liquid povidone iodine all over the lesion and skin around, take anti histamine like Cetirizine or whichever you have.
I hope this answer will help you.
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