Pram assuming this has been an ongoing problem, there could be all sorts of reasons for the baby feeding all the time and not gaining weight. I would guess that the most likely would be that the baby is not latching on properly and is therefore an inefficient feeder. This can cause poor milk supply which can then create a spiral of baby not getting enough and feeding all the time. Although it didn't create any problems other than soreness if she fed more than usual and longer feeds than the typical breastfed baby, I have realised since having DD2 that DD1 most likely didn't have a proper latch although as I say it wasn't bad enough to cause any major problems. My recommendation would be to see a lactation consultant as early on as possible if you have any breastfeeding problems as they will be better able to help you than the NHS MWs who even if they have the knowledge, don't necessarily have the time to give you the right help. But also different babies have different needs so even if there aren't any problems (as there sounds like there may be in this case) some will feed longer or more frequently than others. So for example, I roughly used the GF routines (although DD2's more frequent feeding and unusually low sleep needs meant I had to modify them a lot more for her than for DD1) and DD1 was sleeping through from the 10pm feed from nine weeks whereas DD2 was typically feeding once or twice overnight and having an extra feed in the day until about eleven months at which point she suddenly changed and "caught up" with what had been DD2's feeding pattern at that age. DD2 is taller/heavier than DD1 was and she ate more solid food sooner than DD1 so I presume she just has a faster metabolism and higher energy needs. Sleep-wise, DD2 currently sleeps around 10 1/2 hours in 24 which is loads less than the average child of her age (and less than DD1 has at age six!) so we have to be very strategic about when we put her to bed and how much daytime sleep we allow if we don't want to be woken lots in the night - it took us a little while to cotton on to her unusually low sleep needs so it's also possible that some children who are waking lots in the night are doing so because they don't need so much sleep although obviously there are lots of other reasons why babies might be awake in the night.
Also, Ice is totally right that people mostly post about these things when there is a problem rather than when there isn't which can give a skewed view of the likelyhood of difficulties.
Re: routines and leaving babies to cry, I don't think it is the case that these things are mutually exclusive one or the other things. We have always had routines from fairly early on but not in the rigid "I will not feed you before x o'clock" sense - it's more like how you have meals at routine times but if you're hungry a little early you might eat early whereas if you're hungry a lot early you might have a snack and have the meal at the usual time kind of thing. So for me routine means that in the day time the baby is offered feeds at routine times rather than waiting for them to request them but then after the late evening feed, they've not been fed unless they wake wanting it apart from the early days when I would always wake them after a certain amount of time day and night to make sure they didn't go too long between feeds. And with crying, our eldest didn't like lying down (you could sometimes literally stop and start her crying like one of those toy dolls by changing her between horizontal and vertical) so would always cry when she was put for a sleep but it was more a "registering an objection" kind of cry rather than a distress or an "I need something" cry so we would leave her and probably 95% of the time she'd be asleep within five minutes and the rest of the time we would then go back and try the standard burping, nappy, feed etc to see what was wrong. Whereas DD2 has never really cried unless there is something wrong or she is genuinely distressed so we haven't really ever left her the way we did DD1. And then some babies just cry most of the time no matter what you do in which case sometimes you just have to leave them to cry at times - I am always terrified I'm going to get a baby like that but so far I haven't.
Glad to hear you've finally got your scan Panto but not great that you had to sort it out yourself!
Saw Dr about my boils and he said that the antibiotic I had is the least likely of the ones I could have to make me sick so as long as they're healing up fine without there's no need to have more. He also said that the stuff they would give a longer course of to get rid of them isn't safe for pregnancy so I can't have it at the moment. I should have asked whether it's safe for breastfeeding though as it'll likely be a long time before I can have it if it's not. He sent me for some blood tests though including ferritin which for some reason wasn't done the last time even though the sample was sent for it.
And since I'm feeling better and DH was at home, he got out the Christmas presents for his side of the family and I've wrapped them all ready to hand over when we see them at the end of the month. Except for the one we haven't got yet because obviously I can't.