What can decrease the chances that i can get pregnant?

Age, smoking, STIs: Past the mid-20's, as women get older fertility decreases, so female age is important. Other things that can decrease fertility are smoking, overweight / obesity, pelvic infections like chlamydia or pid, fibroid tumors or polyps of the uterus, endometriosis, surgery involving the ovaries, uterus or tubes, ectopic pregnancies, and cancer therapy. See a rei specialist if you're ttc without success.