Welcome to HCM.
Fluid in Pouch of Douglas (POD) could be due to appendicitis
or pelvic inflammatory disorder. Both these conditions can cause lower abdominal pain
. In addition any bowel pathology also can lead to pain.
More over since you have already had hysterectomy
3yrs back, bowel adhesions from surgery or past adenomyosis / endometriosis
may also result in lower abdominal pain.