Been trying for 6 months

Been trying for six months, I know this dosent sound long but, we have literally had sex everyday . We haven't missed a single day. I have tried before in previous relationships for years. I have one son who is almost two and he is my rainbow. I have had 3 miscarriages . 2 in the early 1st trimester and 1 in the late second . Just don't know what could be wrong , any ideas?