Reflux or spitting up of milk is very common at this age and occurs when stomach contents regurgitate or back up, into the food pipe during or after a meal. At the lower end of food pipe near the junction with stomach there is a muscular valve which is weak at this age. Moreover the diet is mainly liquid at this age & the babies spend most time lying down all factors contributing to reflux. Reflux is also more likely when babies stomach is squeezed from outside as happens when babies cough, cry, or strain or are wearing a tight nappy.Also Overfeeding can aggravate reflux. It is common in infants but most grow out of it. Appearance of milk weather curdled or not has no significance. you should consult your GP if any of the following occur: *Vomiting large amounts or persistent projectile (forceful) vomiting, particularly in infants younger than 2 months old *Vomiting fluid that is green or that looks like coffee grounds or blood *Difficulty breathing after vomiting or spitting up *Refusing food that seems to result in weight loss or poor weight gain *Excessive crying and irritability. Hope you find the information useful.