Second, newborns can wake constantly at night because their brains have not yet regulated their melatonin secretions enough for the child to have consistent periods of wakefulness (during the day) and lengthy periods of sleep (overnight). Thankfully, one sure fire way to combat both of these issues is to make sure that from 7 am to 7 pm, one never allows their newborn to nap for more than 120 minutes at a stretch.
If your newborn has been asleep for 2 hours, do whatever you can to wake them up. Once they are awake feed them while doing everything in your power to keep their eyes open during the feeding. Then, keep them awake for up to 50-60 minutes total and then watch for signs of sleepiness (eye rubbing, staring into the distance reduced engagement, fussiness), and put them down for a nap. If baby sleeps less than 2 hours, simply feed them when they wake up, working hard to keep them alert during the feeding so they take a full feed. The younger the newborn is, the tougher these suggestions may be to implement but keep trying and as they grow older, things will get easier. Limiting daytime sleep to no more than 2 hours at a stretch, and ensuring frequent feeds during the day, will help baby sleep longer stretches overnight.