First off,go to a physio and get a specific diagnosis,it does sound as though you have self diagnosed correctly but definitely get a professional opinion.
In the mean time take complete rest from upper body lifting while initially applying ice to reduce inflammation(ibuprofen is useful during acute stage)then introduce heat and self massage to the area.
Personally i'd let the inflammation and pain subside before introducing rehab exercise,however,the physio will be able to give you the correct exercises and how often you should be performing them.
This may also be useful
http://www.uk-muscle.co.uk/shoulders...exercises.html