Decreased milk supply

Barbara
So my 5 month old just started sleeping through the night and no longer feeds at night. 
Now I've noticed a dramatic decline in milk, my breasts feel empty. They no longer feel super full when I wake up in the morning.
During the day I feed him on demand, on average 5-8 times. 
Has anyone else been through this? I'm a first time mom so I'm a bit concerned, I haven't had any worries or issues regarding milk supply until now. 
Also, will pumping at night help? 
I really want to keep breastfeeding him for a while longer.