Everyone's different. The first milk you get is colustrum. Some women experience leaking early. Some not til later. Some don't leak at all. No way to know when and if you're going to leak.
Well actual milk will be start from 24 hours til 2 days after delivery. But colostrum with is not milk but needed for ur baby's 1st feeding that can start any time from 3 month til delivery. It's different for everyone. The fullness u are feeling is normal it's ur best just preparing for later n the hormones.
Most women start producing colostrum at around 20 weeks. You'll get milk a few days after delivery.