Have big difference in arms.left arm is thicker,stronger.but right arm is thinner,weaker.sometimes right arm is whimpering.what is that?any treatment?

Depends: Depending on which side is your dominant side, it is normal to have normal anatomical variance between muscle mass of each side. However, diameters greater than 5 cm difference is between muscle mass between the two side warrants further investigation and evaluation to rule out underlying neurological disease.

Handedness: There is hemihypertrophy which is present from birth. Is the stronger arm the one you use the most, ie right one for right-handed, left for left-handed? If normal, just need to consciously use and exercise the weaker arm more. Does whimpering mean pain or something else? If pain, need to go slowly to prevent a strain or sprain and build up.

See neurologist: Your left arm is normal while right arm thinner and weak due twosome neurological problem .Right arm problem may have been there since birth or happened later ,due to any injury to neck or any other reason ,.You should consult a neurologist , get investigated and treated as needed