I am vegan, my girlfriend is not. she wants me to quit?

Your girlfriend has every right to be concerned and that is kinda cute..she cares about you. Anyway, don't talk yourself into going back to dairy if you wanna stay vegan. Try eliminating foods from your diet that you may think are causing the pain; for instance, remove soy milk from your diet for a week and stay away from soy products. If you see an improvement in your digestion and gastric health, you probably need to stay away from soybean products. Anyway, that is just one example.