How long are your breastfed babies sleeping at night!

My 16 week old has taken a turn for the worse only sleeping 2 hours at a time at night she wakes up crying I nurse her she falls back asleep for another 2 hours feed her again and so on and so on until about 6 am she'll wake up for a final feeding and crash until about 10 if I'm lucky. Idk what happened at 2 months she was starting to sleep 5 and 6 hours at a time, what should I do? Is it because she's breastfed and not getting enough to eat is this happening to anyone else??! I'm starting to get irritated through the night. I notice if she's in the bed with me she'll sleep a little longer. But I like to keep her in her crib for the most part!