I finished a round of antibiotics ( amoxicillin) for strep throat and although the strep symptoms are gone, i am so fatigued.?

Immune system helps: The antibiotics kill many of the bacteria and prevent a secondary infection of rheumatic heart disease. Your body's immune system does the remainder of the work and can leave you needing rest and recovery time.

Lots of energy used: Having an infection takes a rather large metabolic toll on you. Your body has expended a lot of energy fighting the infection, so it is not surprising that you feel as if you have had the stuffings knocked out of you. You will slowly regain your strength as your bodt recovers from the infection.