sounds like bub is getting enough

DS used to feed for 20 minutes a breast and he ALWAYS fell asleep whilst eating, you just tickle their cheek and they will start eating again

also post feed he always slept...babies always sleep don't they besides eating... It's been two years but that's right isn't it? For at least two months i think, then they stay awake for longer ....

Sounds like you are doing an awesome job, I'd stop all top up feeds..... DS was 2755g at birth and lost weight too, it's normal because they are using so much energy