Since two years, I have been suffering from heavy painin my calf or left leg, only at night. Please suggest a treatment?

Hydration. The first thing that comes to mind is hydration and proper diet for electrolytes. You may also be suffering from restless leg syndrome. I would suggest seeing you local orthopedic surgeon for help in making a correct diagnosis and treatment plan.
Several ideas. A physician can check the circulatory and nerve status of the leg. If things seem okay here, nocturnal leg cramps are a consideration. Mayo clinic review at http://www.Mayoclinic.Com/health/night-leg-cramps/my00410 i've seen good results with simply drinking quinine bitters, but this is something you need to discuss with your physician. Good luck.
Seek a doctor. Possibilities include: venous disease with pain, swelling worst at day's end. Evaluation by a phlebologist is in order. Peripheral arterial disease (pad) is another possibility, and you may be having rest pain, which may be relieved by hanging leg over the side of the bed. Pad is associated with tightening of calf/buttock area when walking. In both cases, a doctor's visit will be enlightening.
Need evaluation. There are many possible casues that include arteries, veins, and nerves. Seeing a vein specialist would probably be helpful. Peripheral arterial disease (pad) is possible and if it is causing rest pain, it is an emergency. More commonly, pad is associated with pain with activity. Start by seeing your primary care doctor.