Ttc in October- January- want boy

Amy • Stay at home mom. Just went back to work part time. beautiful girls. 9 and 2
I am a mom of 2 girls. 9 and 2. They were both surprises, but the 2 year old was more planned. We're trying to get the 3rd and final birthday for August - September 2016. I'm not on BC just pulling out. When should we start really trying?? Also we really really want a boy. it's 50/50 I know but any advice?