I would have liked to know the stage of your initial cancer and the treatment which you have undergone. If the pain is on the same side as the surgery then it could be related to the surgery itself and taking a painkiller should suffice. If it is on the opposite side or if it is not being relieved with painkillers then we need to investigate. A simple x-ray chest should be enough for the moment and will tell us if this is disease recurrence. The black stools are most probably because of stomach ulcers which are quite common. For that you should start Tab Pantoprazole
20mg twice daily for a month atleast + Syp Mucaine
gel 2 tsf thrice daily. That should take care of the problem. Helicobacter Pylori
is not positive in all ulcers.