A dowager's hump is a severe rounding of the upper back. In older women, this change is considered a sign of advanced osteoporosis. The rounding stems from compression fractures of the vertebrae in the upper spine. At your age, it is more likely to be kyphosis, a spinal change seen in adolescents that sometimes occurs among adults.
I would suggest a thorough medical checkup to make sure that your general health is good and that no undiagnosed problem could be responsible for the rounding of your spine. Then, I would recommend consulting an orthopedist, a medical specialist trained to deal with this type of spinal problem. You may need to have a bone density test to rule out osteoporosis.
Kyphosis that occurs in teenagers can stem from slouching and rarely causes pain or other symptoms. A number of medical conditions including arthritis of the spine can be associated with kyphosis in adults. In most cases, the curvature can't be reversed so the goal is to prevent a worsening.
Depending on the cause of your problem, I suggest trying therapeutic yoga or Rolfing, a form of deep tissue massage. Appropriate supplements would depend on what your medical checkup reveals. If your spinal rounding is due to osteoporosis, be sure you're getting enough calcium (for women I recommend 250 mg of calcium citrate twice a day with meals) plus 2,000 IU of vitamin D3, needed to help bones absorb calcium. Here are my other recommendations for osteoporosis treatment.
Andrew Weil, M.D.