Depends. If you have a type 1 allergy to insect saliva, should be gone in 1-2 days. If type 4, could last for weeks.
It depends. If you are not getting rid of the source of the fleas, you will keep getting them. Use an appropriate pesticide (safe around animals) and have your pets treated as well. Avoid scratching and keep all bites clean. Caladryl clear may help prevent itching, and allow them to heal more quickly.