12 week old baby girl sucks on fingers and moves a lot when sleeping but doesn't wake. is she hungry or just self soothing? is it teething?

12 weeks: It is unusual for 12 week old babies to start tree thing at this age. For feedings: just make sure the baby is getting enough formula/breast milk during the day and minimal feedings at niight.

Not teething: Children usually begin teething at about 6 months, and should be taken to pediatric dental specialist (for same reasons you see a pediatric medical specialist) no later than 1st b'day. As to finger sucking, it's a normal reflex. Infants are very oral (btw pacifier less damaging than thumb/fingers). You'll have to talk to pediatrician about nutrient levels.

Might be: self soothing behavior and/or teething. Regardless it is normal behavior and not a cause for concern. Just be glad she is sleeping!

She is fascinated : At 12 weeks of age, your baby will become fascinated with her hands. She will examine her fingers and thumbs closely, put them in her mouth and try to suck on them. She also dreams and recognize your voice. It is very common for this age. All babies are different individuals, and they develop at different ages. Congratulations!

Fingers in the mouth often means self soothing. Hunger may be associated with crying or discomfort. Ensure adequate feeding and monitor weight gain with your pediatrician. Request a copy of the growth chart at the next visit, and immunizations are due at 4 months per CDC guidelines. A video of her sleep pattern may be reviewed during the visit if there is still concern.