Why do some women feel cramps before & during their periods while some don't? a detailed answer would be appreciated

Commonest: Condition is pms. The brain controls a 28 day cycle known as "the period cycle". If this cycle is upset by bad brain chemistry it exercises poor control. This causes pms emotional lability, cramps.Ibs, heart palpitations, nausea etc during the period. It is usually associated with sweet or salt craving that is the clue! it is the result almost always of poor diet, empty calories, sugar, caffeine.

Maybe not detailed!: Some women produce more prostaglandins and thomboxanes that causes cramping. Others do not. This is why nsaids like aleve (naproxen) will help. Neural factors, relating to the drop in estrogen immediately before a period, influence levels of serotonin, also a factor in cramping. This is why low dose ssris have benefit. So it is the differences in body chemistry that causes this disparity!