The commonest cause of vomiting at this age is regurgitation due to overfeeding. Give only breastfeeds at a gap of atleast 2 to 2-1/2 hours,nothing else by mouth,don't wake her up for a feed. Feed 5 mins each breast,burp her well for 10 mins after every feed and keep the baby elevated by placing a cushion beneath the head and shoulders,always. If not improving even after trying the above mentioned instructions strictly,consult your paediatrician for physical examination.