I'm 39 weeks and just started leaking but my breast size is the same everyone is different
Not everyone leaks and your breasts still have plenty of time to grow.
Its completely normal to not be leaking.. Not everyone leaks while still pregnant, some don't start until after giving birth, could even take a couple days after giving birth. And you're still just 20 weeks, your breasts still have plenty of time to grow and even if they don't, its not a horrible thing. Try not to worry so much :)