I am not a vegan, though every once in a while I eat vegan if I'm feeling unhealthy--forces me to cut out dairy and saturated fats.
Make sure you're combining proteins wisely--just because brussels sprouts have protein doesn't make that the same kind of protein as you get in meat, eggs, or tofu. Same with beans--you need to combine beans with rice, or an equivalent, to get a complete protein. This website seemed to be helpful, but there's also a ton more on the web:
All for vegans and everyone else too.
My favorite diet, personally, is no animal products but fish and eggs. Fish is a wonderful protein, and I'm sorry, I can understand feeling bad eating a cow (I mean, it's a mammal after all), but fish seem to have less emotions than plants do. My 2 cents.
But yeah, if you're not getting enough protein--as it seems you're not--try making sure you have the correct plant-based proteins in your diet.