I find a lot of foods cause my stomach to get upset (IBS, i'll stop there) - I can't take oats or wheat or breads...
I have digestive problems as well.... I won't bore u with the details, but I have Celiac Sprue, so I can't eat anything with wheat/gluten. Plus, most other non-gluten grains upset my stomach as well. It sucks, especially being vegan, since it cuts out a lot of your food options.
As for protein, I do soy protein shakes (one per day, with OJ or some other fruit juice to replenish glycogen stores... try Jay Robb Soy Protein Powder), I eat a bunch of tofu (marinade it in Bragg's Liquis Aminos... it's a gluten-free soy-sauce that is low sodium and very yummy!), Hummus (YUM!), Peanut and almond butter (organic) on apples, Soycrips, ANDI Bars (vegan and gluten-free protein bars...delish!), nuts/seeds, and Soymilk (Pacific Ultra... it has the most grams compared to other soymilks: 10g per cup!).
As for the amount u need, it depends on many factors: weight, workout goals, Kcals, amount of activity u do, the type of protein u eat.....
Hope this helps.... let me know if I can help ya out some more!