Hello! I know there are lots of conditions for Shoulder Pain, but after researching, I cannot find an answer that suites my case. I'm 26 years old female, quite active, but nothing too crazy.
I started to feel some pain in my upper right arm (where it connects to the shoulder) about a month ago. I thought I slept in a wrong position and didn't pay much attention to it. But it won't go away! I have full mobility of my arm, well almost... first thing in the morning I have some very hard time lifting it up from 45 to 90 degrees in front of me. It's to the point where I have tears in my eyes while pouring a cup of coffee. No problem lifting it on the side or reaching backwards. The rest of the way it goes just fine and it gets better during the day. But right before I go to bed, it starts again. I cannot sleep on my right side because of that. The next morning I wake up with the pain again.
My neck feels a little tight, but its not uncommon for me and 2 minute massage takes it away. I do not remember any injuries, may be a couple intense workouts, but like I said, I don't do anything to push my body limits, just staying fit.

Your answer will help a lot and would be greatly appreciated.
Thank You in advance.

It is hard to say what is going on. There is a multitude of possible reasons for what you're experiencing.

I would talk to your doctor, or maybe a physiotherapist or Chiropractor.