When my cramps were really vicious, mefenamic acid used to be the only thing that worked.

Since I exited my teens and things improved: ginger tea, abdominal massage, switching to a menstrual cup (some people find they improve cramps a lot, for unknown reasons; a few people find they worsen them), and some specific yoga stretches (chiefly baddha konasana, cobra, danurasana, and quadricep stretches) have all seemed helpful, though it's obviously hard to identify causality when I've simultaneously been getting older and my body's been settling down.