My 2 and half months baby likes to lean her head backwards when she sleeps even when held upright. is this normal?

Muscles: typically, a 2.5 month old infant has poor neck muscle control. The head at this time is the largest single part of the infant, and will need to be carefully supported. At around 5-6 months, you will see increased muscle control and the baby will be able to move the head much more purposefully. if the infant is still having difficulty controlling its head or its muscles seem weak, talk to DR.