Why is it so hard for me to conceive!

Why is it so hard when my mom is so fertile she just had her 9th child at 43! Don't get me wrong I am super happy that is such a beautiful thing, it's been 4 years for me and I haven't been able to get pregnant and I'm only 23:( my sister is 25 and has 2 kids already. I feel fine, but it's time for a specialist, but why me I don't have money to go through fertility treatments :(