Hello  Dear
I evaluated your concern in depth .
@ This much weakness after recovery from 
pneumonia is not normal at all 
@ Possibilities are as follows :
1. Initial diagnosis was not confirm only as pneumonia , it may be having 
    associated underlying pathology not detected / missed by clinician .
2. Pneumonia is still not controlled & pathological process inside the body is
    still going on 
3. Emergence  of new condition during or after recovery from Pneumonia 
@ Moral of the story is that you require thorough history , physical 
    examination , further detailed work up to reach at the root of the issue
    and get final management guidelines .
Hope this will help you definitely .
Feel free to ask any further health related query in future anytime .
Thanks for using Health care magic .
Regards .