2 month old baby not wanting to eat.

She still has pee diapers, and pooped two times today but it wasn't a lot. She eats 3-4 oz every 3 hours and she has been asleep for a while on and off and she isn't wanting to eat and it's time for her to eat. She will suck for alittle bit then spit the bottle out. Anybody have any guesses as to why she is doing this. First time mom so everything that seems so little to others is a very big deal to me because I'm still learning.