Problem in muscles around hips (esp right side) buttock and outer thigh. Feel tightness&stretch all the time (no pain). Cannot sit or drive for long as I feel weak in buttocks. When I do yoga, I feel nice but after sometime, its back to being tight/weak?

Need to examine. It is not feasible to provide a meaningful opinion without taking additional history, physical examination and may be some tests. If you are overweight losing weight would help (easier said than done). You may wish to add some aerobic exercise in addition to yoga.
Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.
Practice safe sex, if you have sex.