How can i gain body mass? P90X?

I'm nearly 17, 6 foot 1 and just under 10 stone so im quite skinny. I've grew about 6 inches in about 9 months which has made me look lanky which i dont want. Im currently doing the P90X workout regime but im not sure if this will gain body mass. I need some quick fix ideas on how to build bulk? please help!