Supplement Help !

Currently I am using 2 supplements ON Whey Protein, and Mammoth 2500 weight gainer. I am supposed to be taking 4 scoops of the weight gainer but i choose to take 2 instead (Been putting on a bit too much fat) and i add an scoop of protein. I take this once in the morning when i wake up and once during the day. After workout i consume the ON whey protein and once more before bed. Would there be any advantages to taking an Isolate protein instead of whey, should i switch? second question is would it be ok to add dextrose to each of those shakes i take throughout the day? My goal is to bulk up as much as possible and add lean muscle mass, currently 15lbs off my target of 200lbs Thankyou for any feedback