TTC for baby number 3

Hello I have 2 beautiful daughters already and I so want another one my boyfriend and I knew each other for 3 years but just recently got into a relationship in March and have been trying every since and still no baby. I use glow and so far still not pregnant. I had a miscarriage in 2013 do you think this is why I can't conceive even though my doctor told me having the miscarriage wouldn't affect my future plans for children.