Psoriatic arthritis

It would be difficult to give a specific answer as to 'what is going on' based on the information provided and without examining the joints. This is because pain in or around joints can have a number of reasons, one of which is inflammation of the joints known as arthritis. Therefore, you need to consult a rheumatologist for appropriate evaluation of your problem. Secondly, 'thin bones' or Osteoporosis would be extremely unusual(though not unheard of) in a young male. Therefore this also needs evaluation, both to determine if indeed Osteoporosis is present and if so, its reason