Child age 12 "perpetual cough" 6 plus wks. original diagnosis micoplasma pneumonia-resolved. 10-12 lb. wt. loss. extreme fatigue continues, whole body in pain from constant ongoing coughing. ?

Get seen again: This needs further evaluation symptoms should not be that bad for that long. May have had more then one infection or weakened immune system may have picked up a second infection.

Concern : I would be quite concerned. I would take back to MD and get infectious disease work up, and be seen hematologist/oncology doc. Chronic cough and fatigue associated a lot of immune depleted patients. Also see if did forge in travel as parasite diseases