thanks for all the support.
the thing is, she is not actually falling asleep whilr nursing, just not really nursing anymore. she is not sleepy at daytime, only sleeping for long stretches if she is in the sling, otherwise she is being awake quite a lot.
we are monitoring her intake today, dp is taking care of the other two so that i´ll have time to stay close to the scale :)
You may like to try breast compressions and / or "switch nursing" when she stops actively sucking. Switch nursing is that you give her the other breast once active sucking stops, and just keep switching breasts for the whole feed. Breast compressions can be seen here: http://www.breastfeedinginc.ca/content.php?pagename=vid-4dayold
Hope the weight gain goes well!