At this age, babies do take out a small quantity of feed (may be a teaspoonful) curdled milk with/without mucus. This is called "possetting". It resolves as baby gets older.
Next Steps
Keep baby upright or burp after every feed for 10-15 mins atleast, avoid tight clothing/diapers at tummy area.
Health Tips
If you feel baby is vomiting more quantity of milk, not gaining weight, chokes while feeding/coughs and becomes uncomfortable post feed, meet your pediatrician to rule out reflux disorder (GERD).