best to visit emergency opd. there duty doctor will decide whether to refer physician/gynecologist/surgeon.
if you are overdue of menses,first rule out pregnancy.and visit gynaecologist
can visit physician as it could be cystitis, gastroenteritis
if unable to pass gas/stools , visit surgeon
Next Steps
to my patient ..after clinical examination i would first advice injectable antacid antiemetic and antispasmodic.
then an ultrasound for deciding further management