Breast milk is easily digested and that is why babies feel hungry more often and may demand feed frequently. If you are feeding the baby from both the breast on each feed then the baby is taking only Foremilk, which is less on calories and less satisfying. It is a good idea that at one feed let the baby completely drink and empty one breast before you go on the second. On the next feed you may start this process from the other breast feed.
When you offer both breast and bottle feeds there is nipple confusion. When the child sucks at the bottle nipple he draws milk. Where as to get milk from the breast baby has to suck at the areola of the breast and not the breast nipple. When this happens, baby gets in to the habit of nipple sucking and does not get milk while sucking at the breast nipple and does not get satisfied.
Also the top feeds are sweater and the breast milk is usually tasteless. It is hard to eat any thing after having a sweet meal.
You also need to know that Breast Milk is fully adequate till an infant is six months old. Exclusively breast babies have lesser number of infections, allergies and also have better developments with better IQs.