Shoulder Tendonitis?

A few weeks ago I injured my shoulder doing some bench press. It never really hurt but just became very weak and uncomfortable. If I used it for anything practical a slight burning sensation made me stop. Ive been resting it for over three weeks now and the burning is almost completely gone but the shoulder is still very weak which keeps me from using it because when I try to it isn't very comfortable. I have a full range of motion but the time it is taking to improve is very frustrating. I cant go to a doctor really cause I don't have substantial health insurance and I dont speak japanese (ive been in japan for a year) well enough to communicate this type of thing. Does it sound like typical tendonitis? This extroridinarily slow healing process?

when I ride my bike and run for cardio my shoulder feels fine, short motions without raising my arms are fine more or less but Im a surfer and that just doesn't fly for me. any movement which involves raising my arm causes the discomfort and the shoulder just immediately feels dramatically weaker. Again I have a full range of motion but after a few moment of moving it around there isn't necissarily a pain but just a discomfort and the urge to stop moving it entirely. I know, its difficult to explain. Ive been stretching, and icing several times daily which makes it feel better immediatly but i cant seem to shake the problem in the long run (relative long run). 

That is when it feels most weak. It has been 4 weeks now since the initial injury and while I can feel a difference from week to week the day to day improvement is minimal. Very frustrating. Ive been doing light exercises like you've described with a water bottle but I'm terrified of making the shoulder worse so I keep far away from pushing myself. In the mornings my shoulder feels restless and and throughout most of the day. Is there really anything else I can do besides wait for it to get better while I stretch and do those exercises?