It will probably surprise you to know that you don't need nearly as much as you might think you need. It's the first question new Vegans usually ask because they are used to getting that satisfied/full feeling from a fair amount of animal protein. The reason for that are the type of bacteria that lives in a flesh eater's gut - they are used to getting their share of animal flesh and fat. When you feed them this, they release some propionate, and you feel satisfied.
Vegans, provided they get enough fiber in their diet, have a different set of bacteria living in their gut. These bacteria are often referred to as the "good" bacteria. They feed on fiber and they also release propionate as well as other beneficial compounds and in greater proportions than the animal munching bacteria do.
Focus on getting more fiber in your diet from whole food products like whole grains, legumes, fruits and vegetables. Unless you are dealing with a heart issue, plenty of seeds and nuts are ok too, although you may find it's a little harder to lose weight if you are eating too many nuts / seeds and their butters because of their greater fat content.
Legumes are fiber rich. They may not be agreeing with you because your system is not used to loads of fiber. With legumes especially, it is important to soak them long enough and cook them. If you are getting them from a can, they are typically already cooked. Give it some time, soak legumes over night, and cook them properly. You will feel some bloat at first, and more bowel movements, but this doesn't last forever and your body will adjust to it.
As for protein, it is way over-hyped, and for the reason above. All plant eating animals that are typically eaten for protein/minerals/vitamins get all they need from the plant world. Most of them, if not all, are not eating the greater portion of their calories from seeds and nuts either. Although these are healthful, there's no need to make them the greatest portion of your diet.