Need help on weight gain?

OK im 6 foot 1 and 141 pounds. I eat like a pig but i cant gain any weight. I am going to MEPS for the Army on the 24/25 and i need to gain about 8 more pounds to make sure i am safely in the weight class. I was thinking about using come Creatine supplements to try and gain a bunch of water weight. And i currently drink a soy protein shake. Does anyone have any idea on how i can gain this weight this fast? Thanks