miscarriage

i just had my second miscarriage in december, it was a blighted ovum, my dr. says that was a fluke because ive been going to him since last april, he has done all these tests and i had a lap. in august and everything seems to be fine, i got pregnant on the first try w/ lupron, humegon and progestrone suppositories, im trying again and im really nervous, could he have missed something? he told me at my last visit that he is very optimistic that i will be pregnant and give birth. i need advice.