The possible causes could be either of the following:
(to be ruled out using an early morning urine sample, at least 2 weeks after the suspected date of conception)
-Infections: Will require a urine examination and a vaginal swab test to confirm/rule out
-Abnormalities in the structure of the uterus
or inner lining (eg. Fibroids, polyps, endometriosis
, etc.). will require a bimanual examination and a transvaginal ultrasound
Hope this information helps.