Here you have all ready mention you have problem with digestive system like constipation, digestion and all. So due this its natural you will also have acidity issue and due to that you will be having there is some thing called as esophageal reflex where basically the acid juice of digestive system travel up in digestive system and creates bad breath and bitter test on tounge. For this you should take anta acid tablet once a day morning with empty stomach for next 30 days at least. Also change your food timining and habits. Have more of fruits and vegitable in diet, also keep your diet rich with fiber. Have good break fast, average lunch and keep dinner minimum preferably before 8:00pm. Also do brush your teeth twice a day and use good tounge cleaner. Have at least 3-4 liter water daily. Do walking exercise for some time at least 15 minutes daily before sleeping. With all this your digestive system problem will recover. Now for back pain it can be related with acidity and kidney stone also. So for this to diffentiate check when the pain comes always with stomach pain or seperatly. If seperatly then it can be muscular as per your explanation. You need to use hot and cold pack to relax your muscles and do regular spinal muscle exercises to improve strength and stamina of spinal muscle. Exercise suggestion should be taken from physio therapist. I am sure you will be fine if follow all this.take care.