Birth Control after Baby?

Megan • Happily married. One 2015 angel baby, little girl born Sept 2016, & one due June 2019.
I finally had my postpartum appointment today (was pushed back because of my hospitalization and gallbladder surgery) and my LO will be 11 weeks on Monday. Anyway, my doc gave me a script for the mini pill since I'm EBF. 
My hubby and I haven't started to be intimate again (unfortunately). Just curious what side effects the mini pill causes. I haven't taken a pill in 4 years. Thanks!