What Does This Habit Of Constant Drooling And Chewing Hands In Infants Indicate?

My 3 month old is drooling and chewing on her hand. My father - in - law is always perceiving those has signs of hunger and telling me I don't have enough milk which is so annoying because she is gain weight and wets 6 diapers or more a day!What do you think?I would also like to know how do I get her to nap and sleep in her crib?Thank you