I've Been Experiencing Intense Preasure That Comes And Goes In

I've been experiencing intense preasure that comes and goes in my left eye making it droopy and hard to keep open. I've seen several eye doctors and even had an mri that came back clean. One dr suspected myesthenia gravis because I sometimes get very weak through out my whole body. Those test came back normal as well. I had eye LASIK surgery in 2012 these symptoms started about 2 months afterward. I not sure if that could be related in any way or not.