I use Nutri Biotic Rice Protein Powder (58 cal./scoop; 12 g protein). You can get it at a Natural Food Store. There is no soy/wheat/whey/corn junk/crap in it.
In order to extract the protein from the rice, they "isolate" the protein from the carbohydrate molecules in the rice to give you rice protein.
It's totally tummy friendly, trust me...I often can only consume protein powder too.
Re: sweeteners. Stevia's pretty safe. I prefer it to Splenda.