I know it really does suck, i've missed a week of school now with mono, and I just recently developed the rash. The doctor gave me amoxicillin cause I had strep at the same time, but changed it to a different antibiotic to avoid the rash caused by amoxicillin. But I developed the mono rash (the symptom that is caused by the mono virus, not amoxicillin, don't worry it's normal, it happens in some mono cases), besides that, it sux! It's all over my body. So far it has lasted a couple of days. In your case, I doubt it is because of the amoxicillin because you took it a week ago. But the best thing to do it just wait it out, I know missing school sucks, but you can't take any medicine for the rash.