Baby missing, husband drifting?

I have been married for 2 yrs and right off day 1 my husband and I have been trying to have a baby, but I'm just not getting pregnant. We've seen fertility specialists and we are both fertile and healthy, but it's not happening naturally for us. We also tried in vitro fertilization TWICE last year, but the 1st time it didn't take, and the 2nd I miscarried after only 4 weeks of pregnancy. It's killing me that I'm unable to have a baby of mine, to give a son to my husband. Motherhood has been my most cherished dream for years, and now that I am married to the man I love, that wish of becoming a mother have become ever bigger.I'm also having a hard time accepting my inability to become pregnant because I have a lot of pressure on my shoulders because my husband's 22 yrs my senior (we're 28 and 50) and I want our baby to be born soon so he can enjoy him. Also I feel pressurised because he already has a child from his previous marriage, a daughter, that he loves more than anything in the world. Please don't think that I have ill feelings for his daughter (because in fact I like her very much and care for her a great deal) but it eats me up inside that another woman was able to make him a father and I am still not. Adoption is not an option, nor is surrogacy, because I want the baby to be HIS, and I want to give it to him, not yet some other woman. And his family is also pressuring me to get pregnant and "produce him an heir" (these are their exact words, what with them being of lebanese origin and having a male child is very important in this culture). And the worst is that now this is also affecting us as a couple; he's being distant and away at work a lot more (he's a doctor) and I think his family might be telling him that I'm not a good wife because I can't give him a son. Lately we've been arguing a lot and bigger than we ever did, and we make love only once or twice a week (we used to do it everynight except the 2 nights a week he's on call at the hospital). Even his ex-wife (who still blames me for their failed marriage) seems to rejoice at the fact that I can't have a baby. I feel lonely and deprived [emotionally, as a wife and as a mother-wannabee]. I want my husband back like we were in the beginning, I want to become a mother more than anything in the world, and I want to fulfill this dream that is also my husband's whom I love to death but I think I may be going nuts. What should I do to make us close again, and to live through this long wait of getting pregnant?