Why?! Why is it so difficult?!

I am 22 years old. My husband is 22. We have been married for three years. We are both healthy as far as we know. I do not have pcos or endometriosis, I have completely regular cycles, I ovulate on the same date every month, we have used preseed, ovulation kits, had sex every other day through the month as well as every day of my fertile period.... Yet we still have not conceived. I'm waiting for my period to come in two days as I am positive I did not conceive this cycle, again. It has been 8 months. Why is it SO HARD to do the ONE THING I have wanted my whole life to do?! I want to be a mother, I want to give my husband a child, I want to be a parent more than anything in this entire world. Why can't we just get it right and get pregnant?!