Is PMS avoidable, or are some women just lucky and never get it?

A/W Dr. Pappachen. Avoid caffeine, chocolate, alcohol & salt. Get GYN eval to R/O underlying pathology. Consider omega- 3 fatty acids, magnesium (supplementation or through diet) or Black Cohosh with dr ok. Sipping Chamomile can dissipate pain.
Both. I'm assuming you mean pre-menstrual syndrome. Of course today being st. Patty's day, we can't ignore good luck/fortune. Ocps (oral contraceptive pills), pre-medication with nsaids, lifestyle modifications, etc...All could potentially help. Get with your ob/gyn and explore this further.