Scattered mind while doing Body Scanning in Vipassana

I have been practicing Vipassana under the tradition of S.N Goenka for the last 2 and half year. When I scan my body and observe different sensations, I find that my mind is not clear and It's not like I'm sleeping but there is dullness of awareness. Some part of my mind is aware of the sensations but it's not clear and there is a thin layer of thoughts in between. It's like trying to see the sun(sensation) when there is thin layer of clouds(thoughts) in the sky. In other words the mind is scattered while doing Vipassana. I believe it's the sloth and torpor that is causing all this and Vitarka-Vicara faculty is not that much strong. I have read some suggestions for this like having the perception of light, walking meditation etc. but none of these are helping me out. I would be very grateful if someone could point out my mistakes and give some advise to overcome this.