Infertility in early 20s

Everyone says "Your 20s are your most fertile years." Just that sentence makes me tear up. I have been trying for a baby for 4 years now. I'm 23 and have tried clomid, bbt tracking, OPKs, and even had an HSG done to make sure my fallopian tubes were open. My SO's sperm is good to go. I know there are many more things I could have done to figure out what is wrong with me but money gets in the way due to tests getting more and more expensive! It's such a struggle, it hurts to see all of my friends getting pregnant and getting pregnant SO EASILY! A lot times I think why me?? I try not to let it get me down all the time but I find myself becoming so envious of people getting the BFP and becoming moms. How many of you are dealing with unexplained infertility and what have you done to over come it?