Hi Doc. I Bf My Newborn Baby For Half A

Hi doc. I bf my newborn baby for half a month..and i bottle feed her lactogen. Sometimes i bf her sometimes i gave her formula. Now she is fully on formula but as she turns 2mth it's hard to feed her now. She kept crying n crying n i hv to pacify to drink. She cn go on for more then 5hrs without drinking anything. Is it the milk??