My daughter is 4 months old. She is a pre-term baby. She is totally depending on formula milk. I am maintaining 2 hours gap in each feeding but she demands after 1 hour each time. If I feed according to her demand then She faces evening colic and vomiting at night. Milk quantity is 60 to70 ml. She is having Similac advanced.It is very hard to maintain 2 hours gap. What to do ? please suggest.