if the injury occurred whist you were doing pull-ups, there is a possibility that you may have strained your biceps brachii muscle/tendon. although not a rotator cuff muscle, it is very closely related. the treatment modality will probably be very similar. the difference may lie only in the course of rehabilitation.
i also agree with heidi that there may be build up of scar tissue around the muscle/tendon and very likely the shoulder capsule. that is why you feel the stretch and symptoms when you put the back of your hand on your waist: the front of the shoulder capsule gets stretched when you internally rotate your arm.
try to get a health practitioner (physio, osteo, sports massage therapist/rehab etc) to examine it. a good practitioner will also be able to provide you with a good rehab plan to improve the function of that joint.
[COLOR="Blue"][B]Billy
Registered Osteopath
[url]www.greenhitheosteopaths.co.uk[/url][/B][/COLOR]
[SIZE="1"]Osteopathic Practice in NW Kent (DA9): Bean, Darenth, Dartford
Ebbsfleet, Greenhithe, Gravesend, Longfield, Northfleet, Stone and Swanscombe[/SIZE]