Any ideas on helping conceive

Nikki

I am 40 I just had a baby girl 7 months ago I also have 4 other kids never had a problem conceiving now me and my fiance are wanting another baby and it's so hard. I am confused. That's y I am on this app to track when I ovlatate but that's not working. I heard about pre seed and folic acid but I don't know what that is or where to get it. Any suggestions plz let me know.