Can you?!

Can you have something wrong with you if you had four kids already? I am been trying for 11 months and haven't gotten pregnant yet. I had some testing last year because I felt like my hormones where off do yo tiredness and acne and test came back good except DHA where a little low which they just told me to get the pill form. I take prenatal vitamins with folic acid and DHA. I haven't went back since.