Constant hands in mouth 3 month old

Does anyone else’s baby constantly have their hands in their mouth? My little one is always sucking on her hands. It’s been weeks now. She full so it’s not hunger related. Even when trying to put her to nap snd sleep she sucks on them. Her sleep has been shorter and her day time naps have become shorter too. Is this normal? We can’t have mittens on her because she sucks those too and she’s learned how to take them off.