It is likely that you may have degenerative changes like osteoarthritis or soft tissue damage.
Make an appointment to see your doctor to give you the correct diagnosis.
A referral to a physiotherapist would also be helpful as they will give you the right type of exercises to do to gently strengthen the arms so that you do not lose any more movement.
This could mean several things. If you exercise a LOT then it could be from that as sometimes the more muscle mass you build the less range of motion you have. This occurs mostly with body builders and others who lift weights in a professional manner. It can also be a muscular condition that is worsening. It may be coincidental but both shoulders may have tendinitis, bursitis, or maybe some overuse injury or injury you are unaware of. My advice is to seek medical attention through your family physician and then go from there. You may need to see an orthopedist, physical therapist/physiotherapist, neurologist, or another medical professional. A chiropractor may be able to help alleviate some of the stiffness and problems you are having as well. Good luck!
Osteoarthritis would not progress that rapidly. If the pain is severe enough and it developed over 6 months to a year, it is more likely something acute that started it. What type of work do you do? I was thinking rotator cuff damage but in both arms seems unlikely unless you do repetitive stressful work with both of them. My differential Dx....Cervical spinal stenosis, cervical herniated disk, or pinched nerve. There are a multitude of Dx that could cause these symtomps without more information and testing it is difficult to say. Go see your PCP and they should refer you to a specialist.