I feel like I have spent the last couple of months glued to this board, every since my son was born.
We have had a few troubles with BF since he was born, he has always been quite fussy at the breast. It is getting worse and worse and it is affecting his weight gain. He is 11 weeks old and last tuesday he was still only 9lbs 3oz (5lbs 10oz at birth), but this was with a week of topping up with a lot of formula.
When I go to feed him he often latches on really well and is feeding efficiently for anywhere between 3 to 20 minutes. However at some point he will always break off for some reason then try and latch on again, this goes on for ages and he becomes more and more frustrated, crying and screaming. When he is actually feeding he is often very squirmy, kicking and hitting me. He is definitely hungry.
Sometimes (rarely) he feeds till he seems full and falls asleep, usually late evening. He also feeds well in the night but he only wakes for about 10 minutes and falls back asleep. He feeds very well from a bottle, and guzzles down whatever expressed/formula milk he is given.
I feel I have tried everything. HV was very concerned about his weight gain so told me to top up with formula, which I have done reluctantly as I don't know how else to make sure he eats properly. She checked my latch, which she said was good as is his sucking reflex, her response to the fussing was that he "just didn't want any more breast" 
. I have also taken him to Breast Feeding cafes where his latch and position have also been confirmed as good by councillors. They were very kind but at a lost to what may be causing his fussing. I've taken him to the GP, who said it was colic and to give infacol which we have and it has made no difference. She checked for tongue tie and thrush and he was fine.
I don't know what else to try. I want to carry on breast feeding (I planned to do it for 12 months) but he is having more and more formula cause I know he is left hungry after failing to feed from me properly. I know this will have a negative affect on the BF, in relation to milk production and that he will end up preferring the bottle (i am worried this is already happening). I am scared of giving it up totally as I know he seeks it for comfort and it is often the only thing that will calm him down (even if he only suckles for a couple of minutes), I also enjoy the closeness it brings. However, the constant battle to get him to feed properly is really upsetting me (and of course him! as well as my OH). The more I try to shove my boob in his mouth the more he screams and the more upset I get.
Does anyone have any experience of this/advice? Sorry this is so long!