Have 100's of mosquito bites everywhere on body. how long will it take for them to stop itching and go away?

Mosquito Bites: Baking soda mixed with a little water then placed on the bite area is a cheap and effective way to help reduce the itching. There is a product call Ben's Afterbite that makes it easy to apply. You could also use Benadryl (diphenhydramine) or Hydrocortisone cream but given the bites are extensive, I would hesitate to place this amount cream all over your body. It can sometimes take days for the itching to stop.

Not too long: These should heal up quickly, most times they are gone in one two three days unless you scratch hard and create a break in skin which can then get infected. So keep your finger nails trimmed