Women,,, explain how i find the G-spot?

So the other time I was getting laid I went down on a girl and tried using the wrist motor on her. Neither way did she squirt. Im pretty sure I was doing it right, medium speed strokes with two fingers facing upwards about 2 cm into her vagina but she just told me after about 20 minutes I was doing it that she started to get sore and like I probably wasnt touching the right area. Is this common? I thought the g-spot was behind the roof of the labia. Theres nothing more satisfying than making a girl squirt using your tongue or fingers and i feel like im missing out