Hi FouraFriend, Here is what you need to do. First feel the Area around the bite, is it warmer that the rest of your skin? Is it oozing any liquid? Are you feeling sick(headache,nausia, flue like symptoms)? if so you need to see your doctor.
If not.. Take a pen and draw a circle around the bit (a little over the red swollen part) if the red swelling continues to move outside the circle you drew you need to see your doctor and inform them of how fast the swelling increased.
In the mean time use a topical antihistomine or a benedryl and it might help with the reaction to the bug bite. Cold water helps or a mix of bakingsoda and water to help draw the venom ( if it has venom) out.
I would not freak out though, some people's bodys and depending on the bite just take a little longer to heal.