How Are Insect Bites Treated ?
From the history given it seems that you have had a insect bite.
First and foremost, If the bite had occurred very recently, then the signs of swelling with severe throbbing pain, itching and redness is a form of inflammatory reaction to the insect bite.
To reduce the redness and pain at the site of the bite, application of ice is adequate treatment.
Clean the area with soap and water to remove contaminated particles left behind by some insects. These particles may further contaminate the wound if not removed.
Refrain from scratching because this may cause the skin to break down and an infection to form.
Additional Nonsteroidal pain medications like Naprosen or Ibuprofen will help to reduce the pain and swelling.
You may treat itching at the site of the bite with an over-the-counter antihistamine such as diphenhydramine (Benadryl) in cream or pill form. Calamine lotion also helps relieve the itching.
Increasing redness, pus drainage, or streaks up the arm or leg would indicate secondary infection, and would require treatment with antibiotics.
In case the pain is very intolerable, you might consult a doctor or visit the nearest ER for a examination and appropriate treatment.
I hope this helps to answer your questions.
In case you have additional questions or doubts, you can forward them to me, and I shall be glad to help you out.
Regards.