Trying to conceive but can't?

my bf and i who are planning to get married, are also planning to conceive a baby. whenever i am ovulating, is the actual time i end up having with him. 30 days later, i always end up getting my period, why is that? i am having while ovulation, i don't know why i'm ending up with my period 30 days later. all my other siblings have kids except for me. i know i have to see a fertility doctor but i want to understand the process before going to the doctor so i don't look like a dumb azz.