Ttc for 8 months

I'm not sure what I'm doing wrong. We BD every day during my FW and have had no luck. I'm 21 yrs old with no children and he is 26 and has 3 children from a previous relationship. Please give me any advice you have! I want this more than anything. When people used to ask me what I wanted to be I replied with "a mother" I know that being a mother is my calling but just don't know what I'm doing wrong to become one! Please help