trying for our rainbow

I've had 2 miscarriages since getting with my fiance of 5 years next month, we each have a child, his Nicholas is 14, my Arabella is 7, our most recent miscarriage was in December 2017. we both know our "parts" work because we each have a child we were looking to unify our family with a baby in 2019. We're getting frustrated by the lack of results, we're almost 31 (me) and almost 34 (him) we both were young and stupid resulting in our existing children, we're ready to be responsible and have put getting pregnant #1 on our priorities. My 7 year old has asked for a brother and a sister, well technically she has a brother he's just twice her age... We're starting to feel like we're just not meant to have another baby.