Sunil: You're fortunate not to be driving in a right lane county, otherwise you could have veered in front of oncoming traffic. From my experience with older style drum brakes, here's my guesses, from most likely to least likely:

1: right brake is not adjusted and essentially only the left is working
2: air pressure in your left front tire is much lower than the right hand. I assume you have identical tires on all wheels.
3: there could be glazing on the right front linings to make them less effective
4: leaking right front wheel cylinder has coated brake linings, making them useless and must be replaced. You should examine the backing plate, where there is a vent for excess grease to escape
5: rear grease seal failing and letting grease inside the brake drum
6: blocked or pinched right flexible brake hose. You did not mention any loss of brake fluid, so these may be not your cause.

If you remove the drum, then any excessive wear on the brake shoes, or any foreign matter should help to pinpoint the exact cause. Good luck and let us know what you find as the cause.
--
Cam a.k.a. CVOLVO.COM