K.L.
You have alot of factors to consider.
1. Is your baby jaundice? If so and it is getting worse then they will be sleepier. If this is the case then you need to call her pediatrician.
2. If not jaundice,is your milk in? If not try supplementing with formula for 1 or 2 feedings.
She should be eating for at least 10-20 minutes, as long as she is full term and your milk is in and she has no other problems(preterm, low birth weight) then she can go 2-3 hours between feedings.
If you still have questions try calling the hospital where you delivered and they can get you incontact with a lactation nurse.