is it okey to take pain reliever for my back pain...

Is it ok to take pain killers continuously ?
No , in your case , the pain you have seems to be chronic been as it's due to gallbladder stone that should be treated . and you have to know the stomach ulcer maybe caused by the chronicity of using pain relievers , that may also lead to Gastritits m upper GI bleeding and so many un-wanted side effects 
How to treat Gallbladder stone ?
the treatment in this case depends on the clinical picture that you have , if you disease is silent with no complain it need no intervention but as long as you have sever abdominal pain that referred to the back that means the disease is active so you have to visit your surgeon to assess the condition such as the size of stone then you might be advised to undergo surgery to remove the stone and the gallbladder specially if it was inflammed , otherwise he might prescribe you a medication to dissolve the stone and to stop having fat in your meals 
What invetigations have to be done to diagnose ?
this includes Liver function tests such as AST ALT Bilirubin ,also CBC to figure out if there was an inflammation going as well as you will have to do abdominal ultrasound to figure out the presence of inflammation and the size of stone
What are the symptoms ofGallstone ?
Right sided abdominal pain 
back pain 
shoulder pain 
nausea and vomitting 
Advice :
have a visit to the surgeon