How do I prove hidden income by my ex to modify child support?

I live in Oklahoma, the child support agreement was made when we had joint (2008), I now have sole custody (2012). His is based off of minimum wage and he has take 6 trips this year, Vegas, Mexico, New York just bought a boat that sleeps 10 people, he says he works at a landscaping business and just bought it so he owns it. Awhile ago my son mentioned he bought land in CA, gave his friend 5K to invest in a salsa business and he posted on facebook he bet almost 4K on the superbowl this year. Is this enough to request a review of his assests and bank accounts? He uses mainly cash is the other problem. I'm very frustrated to be getting $200/month when he is living a lavish lifestyle and not working. How do I prove he is overspending what he doesn't earn and is lying?