RBB on EKG is a normal finding without underlying cardiac D also suggested by N ECHO
.Recent lung infection
can make one prone to develop reduced lung capacity especially on exertion so you will need to take it easy till you recover fully.
Good diet with lot of protein & multivitamins will help.
I suggest you must get treadmill test done in order to rule out possibility of underlying cardiac ischaemia ( low blood supple to heart muscle)