Improving the diet and taking fish oils, calcium & vitamin D can help relieve PMS.
A healthy plant-based diet high in omega-3 fatty acids eg fish oils may help reduce PMS and the intensity of cramps. A high intake of dietary vitamin D and calcium is associated with reduce risk of PMS.
Calcium and vitamin D intake and risk of incident premenstrual syndrome. Arch Intern Med. 2005 Jun 13;165(11):1246-52. http://www.ncbi.nlm.nih.gov/pubmed?term=Arch%20Intern%20Med%202005%3B165(11)%3A1246-1252