When I started using the q- var for my asthma I never loose any weight even if I go on diet or exercise. Is there any factor that using q-var can gain weight.?

Systemic... Systemic steroids can lead to weight gain but, inhaled steroids are used because very little of it is absorbed systemically, thus avoiding this side-effect.
Rarely. Any inhaled steroid can have systemic effects if taken in high doses. However, another cause of your difficulty with your weight may be present, talk to your physician.
Q-var with weight. Q-var is very good medication for asthma. It is a steroid with very little absorption into your body. I would believe that there is very little chance of it causing a weight problem.