Small eater

Dear Sophie is such a small eater and drinker that I can't help but worry that she may not be getting enough. She drinks about 15 oz of milk a day and she has cereal twice a day but even that is a struggle for her. She takes more than an hour to finish 3 oz of milk each time. Feeding time is always so stressful for me. She doesn't seem to enjoy milk and food. Most other babies I know finish their milk within 5-10 minutes. Sophie really test my patience. I am going crazy. Why are you such a difficult baby? Please be good and finish your milk/cereal :(