Feeling like less of a woman

My husband and I both have kids prior to our marriage (he has 2 and I have 1...all of them are infants) We've been TTC for 6 months now and its getting frustrated. We have even argued about it to the point where he leaves the house. I just feel like I want our marriage to be blessed. We spent so much time having kids with the wrong ppl (ppl who we both wish we had never met) and now that we're both happy and are in love, we're finding it hard to conceive. I just don't understand how the other babies popped out like popcorn and now we can't even get one together. He tells me all the time that I should be grateful for our blended family and that the kids are all ours and should be loved equally. Don't get me wrong i love all the kids but its not the same as us having our own. My daughter looks like the spiting image of her biological dad and his two kids both took after their mom (his daughter has his hair and skin color, but that's it). So we have no real piece of us and its killing me. My periods are regular, I know when I ovulate, we've been having sex every day for the past few months. We're doing everything right and doubt were infertile b/c we both have kids prior to our marriage. Every month when I see a negative test, breaks me down. I can't function, think straight, and my mood changes from positive to negative and makes me feel like less of a woman. I'm tired of crying and pretending that all of our kids come from just me and him instead of being step kids. Can anyone relate??