I've been TTC since last July!!!!

Help!!! My husband and I have been having unprotected sex since July of last year,  I haven't gotten pregnant one time and I'm actually trying to.  I have a 14 year old, a 8 year old and one that would've been 10 as well as a mc in 2015.  He has one child who is 8 that everyone wonders the paternity of.  What can I do to help our process, what could we be doing wrong?  Any and all help/advice welcomed please and thanks in advance!