What Causes Persistent Pain In The Shoulder?

Sir, for the last 2 years I have been suffering from shoulder pain on my right hand. It was located in the armpit initially and then it spread to the top of the shoulder towards the front. The pain always gets worsened during night and I find it very difficult to sleep. I approached a neurologist a few months ago and he examined thoroughly and told me that I have water accumulation(I don't know its medical term) on the shoulder and prescribed physiotherapy which I haven't yet started. Sir, what is this condition named? Will I ever get my shoulder back to normal condition? Is there any tablets for this condition I mean water accumulation on the joints??