For ever waiting..

So my boyfriend and have been together for 5 years and now trying to get pregnant for over a year and nothing. I have 2 children from my previous partner my youngest is 8 yrs old. My boyfriend keeps joking about the whole situation. He's never wanted to have any children before until he found the girl he would love to marry. I was have tried everything and nothing.. Now I'm worried that something is really wrong with me .