Hi laundrylover. My ds2 was tongue-tied, but I only noticed it at 6w when he gave this huge smile and it was so obvious, was embarassed not to have noticed before!
His feeding was fine initially, not quite as good as his brother, but not bad. But over the 6 weeks it had begun to get worse. In the 2 weeks before I saw the tie, he had started doing everything typical of a tongue tied baby - struggling to latch, furiously shaking his head, hurting my nips, feeding more frequently because he wasn't getting as much, and getting more and more windy (because he was taking in more air).
It is apparently typical for feeding to be ok, then get worse - because as your boobs become less engorged, the let down is less forceful and they have to work harder to get the milk.
In ds2's case, we were lucky to see a specialist very quickly (in Newcastle) and she said it was quite severe, because especially his upward movement was very restricted - which is v improtant for the latch. She snipped it then and there - said most babies don't feel it and usually doesn't bleed. Of course, he screamed and bled. Not for long though, and his feeding had started to improve by that evening, and within a week was so fantastic - I hadn't realised how bad it had become. He even slept through (well, 11-5) for the first time. So glad I got it snipped, though is always a personal decision for the mum. Dr Sears website has lots of info. Also look at Hunkermunker's bfeeding blog.
Sorry this is such an essay, is a subject v close to my heart but off on holiday shortly so wanted to get as much infor down as poss for you! Congrats to your sil btw!!