On day 3, is your milk in yet? Babies feed like little gremlins right before it comes in, to encourage it. And then in the day or two after - they literally change colour from gorging themselves! Turn from that lovely newborn pink to a different shade.
It won't be like this forever, promise.
Make sure baby is getting lots of milk in the time they're latched. To keep them awake strip them down and use a cold cloth to gently wipe their feet if you have too. Or rub the inside of their palm with your thumb.
It's usually one side per feed, but that never worked for me. A lactation consultant told me to treat it as dinner & dessert - main feed off one side and dessert off the other. Then swap sides for the next feed.
Sometimes babies don't like laying flat immediately after birth either. Especially if it was assisted, or had complications that could give them an uncomfortable neck. I had this with my eldest.
Trapped wind can wake them up shortly after putting them down too. Are you hearing wind release or gurgle up before you pop them to bed?
Like PP said this is a survival instinct too. Until this settled, I had my DH take a shift of holding the sleeping baby so I could sleep too. If that's not an option, swaddling and making sure their cot is warm enough. (Not too warm obviously, some babies don't like being transferred to cold sheets.)