Hi Teddy

It is my belief that what you are experiencing is the beginning of
lymphedema. This is based on what you shared and that it just doesn't
sound like either arthritis or tendonitis.

Here are some symptoms of arm lymphedema:

A feeling of tightness around the arm on the area that was treated for
cancer,
Decreased flexibility in a hand, elbow, wrist, fingers, or leg,
Difficulty fitting into clothing,
Tight fit of a ring, wristwatch, bracelet, or shoe,
Weakness, pain, aching or heaviness in the arm, legs, or feet,
Skin that looks shiny, has fewer folds, and feels stiff or taut,
A dull ache in the affected limb,
A feeling of tightness in the skin of the affected limb,
Difficulty moving a limb or bending at a joint because of swelling and
skin tightness,
Pitting (small indentations left on the skin after pressing on the
swollen area)

These pages can also give you some info and many resource links for arm
lymphedema:

Arm Lymphedema
http://www.lymphedemapeople.com/thesite/arm_lymphedema.htm

Lymphedema and Breast Cancer
http://www.lymphedemapeople.com/thesite/lymphedema_and_breast_cancer.htm

Wish you the best!!!!
Pat O'Connor
Lymphedema People
http://www.lymphedemapeople.com