27 weeks & not leaking?

K
I'm starting to freak out, since my 1st trimester I've been stressing about not being able to breastfeed. 
I'm 27 weeks pregnant with baby #4 and yes I breastfed all 3 but had trouble producing milk and also had no patience so I gave up at the 3-6 months mark. 
But I had my youngest at 21 yrs old so I am much more mature this time around being that I am now 34 yrs old (I personally was immature at 21) and only want to exclusively breastfeed God willing.  
The reason I think I'm gonna have trouble again if not worst is because I'm 27 weeks and still haven't leaked not 1 drop and there's no sign of breast milk preparing.
Is there anything I can do to prepare my breast for milk production?
Any advice will help or would love to hear your experience, thanx in advance.