endometriosis?

Wh
So for the past few years I have had terrible cramps on my period. I throw up, pass out, can't stand up straight.. you name it.
I went and got checked out for endometriosis, after an internal sonogram, they said they didn't find anything on/wrong with my ovaries.
I exercise daily, drink a gallon or more if water daily, eat healthy.. I just don't know what this could be. I go home early from work, and sometimes don't even make it in just because of this.
Does anyone else have this problem or know what this could be?