Hi, Thanks for writing to Health Care Magic, I am Dr Asad Riaz, I have closely read your question and I understand your concerns, I will hereby guide you regarding your health related problem. backache n constipation have multiple reasons ... like backache can be due to either muscular spasm,Truama to back, disc slip etc,while constipation may be pathological or functional in which no cause is there ... black stool indicate blood in stool most of time or it can be black due to iron supplement which also can cause constipation too... if u were my patient I would like to ask detail history since how much time u having black stool n constipation, is ur backache hurt with movements, etc.. do proper exam n run some test like cp to look for blood loss, lfts to look for liver injury , endo copy to rule out PUD, colonoscopy to see any serious pathology like polyps, diverticula etc... Bcs some time these structure can have blood vessel that can cause bleed most of time it s fresh but it can be mix with stool giving colour of black ... n after it I ll manage u accordngly , will ask to drink plenty of water n take stool softener n fiber diet ... if bacakache is muscular then will give some OTC analgesic or will do X Ray to rule out collapse or major pathology .... I hope this answered your question, if you have more feel free to ask. Regards. Dr.Asad Riaz. General and Family Physician..