I have had endometriosis for several years. The first few years my period pains grew more and more intense. At the worst I was in agony for three days every month, and in moderate pain/considerable discomfort for the rest of the month. Painkillers rarely worked at all.
When I cut out wheat and all grains containing gluten, my period pains lessened considerably, and I am now completely pain free for 26-27/28 days every month. I still miss one day of work every month due to period pains, but cutting out wheat and eating healthily has given me my life back. Painkillers also work much better now.
In addition, I take quite a few supplements and make sure to eat a healthy diet, with lots of fruit and veg, nuts, and fiber. The most important supplements are vitamin C, evening primrose oil and good quality omega 3.
Beware that it may take weeks, even months, for this to give full effect. For me it was more than a year before I gained my present state of health, but I hear from others that they generally experience effect sooner after cutting out wheat. I know that the regiment works, however, because of the few times I have eaten wheat by a mistake and been in a lot of pain for days afterwards. I once went on holiday without my supplements, and within three days abdominal discomfort started growing, increasing day by day until I got my hands on vitamin C.
To be honest it is quite a bit of hassle to always mind what I eat and don't eat. But when the alternative is giving up on my life (my job, an active social life, excercising), it is still the easier path. I have also come to embrace the fact that a varied and healthy diet with good quality ingredients is a more delicious way of eating! I eat lots of healthy fats, never skimp on calories, and try new foods all the time. It is a rich way of eating.