Trying to get pregnant

Me n my partner have been trying to get pregnant for 4 years, 7 miscarriages later n hospital has just decided we need some testing done to help us although that last on 25.3.14 is still very much tromatic for me I still need to keep trying, I live to be a mom, I find it the most satisfying thing in life, and yet it's not happening, after I have 3 wonderful children to a previous relationship and my partner has none, is there something wrong with us for us not to be blessed with a wonderful little baby, I can't think of anything more rewarding than sleepless nights nappies etc is there anything we can do to help us along with pregnancy?