I was recently diagnosed with gallbladder pancreatitis but when i lie on my back i feel this hard mass in the centre of my upper abdomin like by the liver and gall bladder. what could that be?

Not likely gallbladder but could be liver. I would verify with local exam by health professional. Show them what you feel and see what they say it is. Can be a number to things such s constipation but need exam. Not urgent.

There are many organs in that area, including the liver, pancreas, gallbladder, stomach, and intestines. Depending on the circumstances, any of them could be palpable if you are thin enough. You should see your primary care doctor and show them the area that you are talking about. If you are feeling something new, I would not ignore this. Good luck.