What Causes Constant Upper Abdominal Pain?

Hello, I have been having issues with what may be a muscle strain in my upper right abdomen, below my rib cage that s been pretty much constant for about a year now - it hasn t gone away. It gets exacerbated if I stretch the wrong way, and when it s at its worst, makes sleeping on my left side difficult. I looked up hiatal hernia, but it doesn t seem to be that condition. I had wondered if additional exercise with sit-ups/stomach crunches would help, but when I d tried this, the symptoms still didn t go away.