My 4 month old has been consuming less milk from 3 days. She would normally take 800-900 ml but her intake is reduced to 600-700 ml in 24 hours. Also, I have been noticing that she pushes the bottle out to suck her thumb & after 5 seconds she again comes back to bottle & does this back & forth. What could be the reason here? P.S: She is dripping in saliva these days