DS had a posterior tongue tie that was missed by the midwife, breastfeeding HV and GP, despite me asking them to check for it specifically.
I was in a lot of pain, and had the classic wedge-shaped nipples with a compression ridge and bleeding. DS was putting on weight well (always around the 91st centile), so I was told that even if he did have a tongue tie, it obviously wasn't causing a problem - as if my pain didn't matter! At the 6-8 week check, I asked the GP to check for a posterior tongue tie (I could see it was an anterior tie). He poked DS's mouth with a tongue depressor while DS was screaming and said there was no tie. I knew he couldn't rule it out visually, but I felt so defeated and tired, I couldn't push him to check properly. Despite me telling him I wanted to breastfeed, the only help my GP gave me at the time was to tell me to switch to formula if it was too painful to continue, and that DS and I had had all the benefit of breastfeeding by that point.
The midwives and HVs kept telling me his latch was fine, even though they could see how mangled my nipple was after a feed. The breastfeeding HV was useless (the number of times I heard her telling people to use formula, it would have been easy to forget that she was supposed to be offering help with breastfeeding). They really didn't care as he was putting on weight. One even told me that even if the GP had found a tie, they wouldn't do anything about it. She showed me the advice they were given about tongue tie - 3/4 of an A4 sheet of paper that didn't even mention different types of tongue ties, and didn't have any advice on diagnosis, not even a diagram.
The day after the GP visit, I hired a lactation consultant. It truly was a last ditch attempt, and I knew I would be out of options if she couldn't help. I couldn't really afford it, but I didn't know what else to do. I was at the stage where I was dreading DS waking up in case he was hungry. It was a miserable place to be.
From the phone conversation she told me she strongly suspected a tongue tie, and when she visited she listened to my symptons, watched him feed, saw my nipple afterwards, felt in DS's mouth and told me she was about 99% sure he had a posterior tongue tie, but that it was difficult to feel it properly.
She gave me the details of the nearest few doctors who would snip the tie (none in my county, but I didn't mind travelling). She could have referred me to a couple, but the one who could see me fastest (Mr Patel at Kings College) needed an NHS referal. She really helped me, not just with her diagnosis, but by giving me a bit of strength and confidence back. Having someone on my side, letting me know I wasn't going mad, made a huge difference.
I got all the details from his secretary and his fax number. I then went to a different GP with all the info and the diagnosis, and told her I needed her to fax the referal that day. She told me that even if DS did have a tongue tie, I shouldn't really expect anything from having it snipped - that it wouldn't make a difference. She also mentioned the fact that DS was gaining weight well - more proof that his tongue tie wasn't a problem 
She did send the referal though, and Mr Patel was great. He explained that it was common for tongue tied babies to gain weight initially - that for the first 3 months milk production is largely hormone driven. In fact, I had a bit of an oversupply which was working to DS's advantage as he wasn't having to try too hard to get milk. He told me that after 3 months some women experience further problems, as milk production becomes based more heavily on supply and demand. As the baby isn't feeding efficiently, the supply can be affected.
The snip itself took seconds. DS was very upset and angry, but fed right away and calmed down really quickly - in less than a minute, I think. There was a slight improvement initially, and I worried that it had all been for nothing, but over the next few weeks things kept improving. DS was 11 weeks when he had the snip, so I was warned that he would have developed lots of bad habits to compensate for not being able to move his tongue correctly and that it would take time for him to break those bad habits. He did learn to feed properly though, and within a couple of months it was entirely pain free (it was much improved within weeks though, just a bit uncomfortable).
He is now 11 months, and we are still going strong.
It makes me so cross whenever I read a tongue tie thread here. It seems crazy that something so easy to treat is still causing such a problem. I wrote to my GP's surgery, and the PCT, not just to complain but to urge them to review the way it is treated locally, and to stress the importance of better support and information for breastfeeding mothers.
Phew! that was long. Great idea Wholelottalove :)
I found this useful.