My LO has just started doing the same. She is 11 weeks. Seem to have it sorted though. If i feed her sat in her chair and she stays in there for about 20 mins afterwards she seems to be fine. If i feed her on my lap then she is sick, no matter how big or small the feed is. Also seems to depend on time of day, which may be if she drinks too fast. On a morning she always brings her milk back up, but she drinks so fast after being asleep. As the day goes on she gets better and her evening feed she drinks down fine and i put her straight to bed with no problems. So I just do her moening feed in her chair!!!