Irregular periods! TTC!

Okay I had my daughter a year ago. I had my period Oct Nov. Dec. Then I didn't have a period til I started Prozac it started the same day I started taking it April 4th(which I only used for one month). Then my period was 2 weeks late in May. Now its June and it's 17 days late again. Why does this keep happening? I'm ttc but it's very hard like this.