Astrid, she may have reflux - when she was at the breastfeeding clinic was she feeding alot? Of course if their tummies are too full, they will overflow, into the mouth which is acidic and could irriate her - as well as being hot... definitely try the upright thing - roll up a couple of towels and place them under the head of her mattress in order to help with the reflux a little - but she sounds a little unhappy and who wouldn't be from having boob shoved into their mouth despite being uncomfortable with it (and mum too!)

I had the same problem with my two who were little babies - all the midwives would try and shove my boob into their mouths and they were just so tiny they couldn't get it all in. I followed my own instinct with Elijah though and it was much better - ignored all those telling me to shove more boob in. He's a big boy - put on stacks of weight before he was even discharged! If you get really stuck, let me know and I can recommend some fantastic, gentle lactation consultants - Pinky is one now too.