Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your health concerns for your son.. As per your complain due to insect bite there have been an allergic reaction at the site of bite due to the poisonous chemical left by the insect under the skin from its stinger while sucking blood.. The symptoms that appeared are due to the allergic reaction to the poisonous venom.. Mostly it is a localized reaction and remains confined to the area where the insect bite has happened.. In case if there are extended symptoms involving other parts of body or showing any other signs like itching on the body, rashes,fever, vomiting,dizziness etc you should consult an emergency room.. If it is localized you can give him allegra by consulting a Paediatrician or physician asking about the dosage as you have not mentioned his age here and dosage is age dependant.. You can do cold compresses over the bruised area.. In case of pain OTC painkiller like Advil can be given.. Hope this information helps and thanks for writing to Healthcare Magic.. If you find the answer helpful please give a Five Star Review and click on found the answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora..