What weight gainer are you using? The easiest one on my stomach is ON pro complex gainer. Not super thick like all the other weight gainers.
ON Pro Complex Gainer is a good product. It has aminogen and carbogen to help with digestion and assimilation.
VPX's Stealth is also a good one that seams to mix easy and is easy on the stomach. I really like the fact that Stealth contains PeptoPro which is a Casein Hydrolysate and quickly enters the bloodstream and vastly increases overall protein synthesis.