A left sided lower abdomen pain with gas and bloating sensation can be probably because of premenstrual syndrome most likely if you are in the last week of your menses. Secondly, likely chances of gastroenteritis is high as it presents with diarrhea and similar symptoms. Thirdly pertaining to fibroids if the fibroids are large they can cause pressure symptoms on rectum and hence bloating and pain.
You may visit your physician for a ultrasound to look for a likely mechanical cause in form of fibroid or an enlarged ovary and also a bimanual pelvic examination to rule out any parametrial cause.
I hope i have answered your query,
wishing you good health,
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