Right shoulder pain when brisk walking/jogging on treadmill

I am a 28 year old female, 5'5" and currently trying to loose weight through excerises and diet. I have been using the treadmill every day for 3 weeks now, and I do 4 miles a day of brisk walking (3.9 mph) and jogging (4.5-5 mph). For the past two days, i have experienced pain in my right shoulder, but no where else. I can breath fine (I am just getting over a chest infection though) and do not experience pain elsewhere. Any thoughts?

[LukeL]

If you are walking outside and it is somewhat cold out you may be clenching your chest muscles and this could put strain on your shoulder causing the pain. the pain could also be from favoring one side of your body when you walk.