I've been taking 2 amoxicillin pills everyday for 5 days and had an allergic reaction. I have a rash all over my body, how long will this last?

Days. Typically drug allergic skin reactions such as hives or pinpoint rashes will begin to improve within 2 days of stopping the drug. The rash will then gradually improve over the next several days. With treatment, the course may be shortened and symptoms milder. Be sure to let your doctor know what is happening!
Depends. Its just wait and watch, may be a few days to even weeks. As long as you have no sob, throat swelling (signs of anaphylaxis), you are fine. If the itching due to the rash is bothersome, take Benadryl (diphenhydramine) over the counter. You may even need steroid pills (prednisone). Of course, stop the amoxicillin.
If. If this is from the Amoxicillin it should disappear in 1week. See dermatologist to discuss treatment options.