should I be concern thatmy baby is 3 months and is just eating 3 oz ????

no, I had the same problem when breastfeeding she would suck for a few minu des and crash right back out. the doc said its just a bad habit of hers. eating till she is comfortable and falling back asleep. he said put a cold wipe on her or take her clothes off and keep offering her the food.

are you breast or bottle feeding?

My four month old drinks four ounces. I don't think you have anything to worry about. They have pretty small stomachs!