For months have had a lot of muscle stiffness and pain in upper right arm, sometimes making movement difficult and some tasks not possible ie putting on clothing. Not the result of exercise and just this one area nowhere else. I'm left handed and aged 70. Could it be arthritis even though it feels like just a muscle problem? anti inflammatory pills do not seem to make much difference 

Many times an arm issue can be due to a shoulder or even a neck problem.

I would go to a Doctor and get a proper diagnosis.

Google Nerve Impingement or shoulder impingement

 

Or take a look here & try the tests they show to see if you have a range problem like they describe

https://www.precisionmovement.coach/sprained-ac-joint/

 

If you have problems for months, why don't you go see a doctor?

I had a friend who had similar symptoms but as it turned out it was because of excessive jerking movements with his right hand, not sure if this information is any help to the Op...

21 minutes ago, ezzra said:

I had a friend who had similar symptoms but as it turned out it was because of excessive jerking movements with his right hand, not sure if this information is any help to the Op...

A lot of people here have "friends" My friend is having the same upper arm pain but with the left arm. it all began after taking the second dose of covid vaccine.

Try an orthopedic pillow...

 

Likely either a shoulder problem or problem in the cervical spine. either way, a nerve may be compressed. you need to see an orthopedic specialist. Where in Thailand are you?

2 hours ago, ezzra said:

I had a friend who had similar symptoms but as it turned out it was because of excessive jerking movements with his right hand, not sure if this information is any help to the Op...

I said I am left handed

1 hour ago, Sheryl said:

Likely either a shoulder problem or problem in the cervical spine. either way, a nerve may be compressed. you need to see an orthopedic specialist. Where in Thailand are you?

Bangkok/Samut Prakan I would see a Dr, finding a good one is the problem

Could be anything from slipped disc (cervical) to shoulder injury or even a torn muscle. Best go see a doctor or orthopede.

10 hours ago, clivebaxter said:

Bangkok/Samut Prakan I would see a Dr, finding a good one is the problem

 

I suggest you see this Harvard-trained specialist in shoulder issues:

 

https://www.bumrungrad.com/en/doctors/Mason-Porramatikul

 

If he thinks it is spinal rather than shoulder in  origin he may refer you onward but start here. He is very good and very nice as well.