Can endrometriosis dissolve. Reason.

I am 21 old having very bad and strange pain at bottom part during my first day of period. I am suffering from it from 6-7 years. When I had my ultrasound 4 months before, gynecologist said I m having endometriosis and prescribe some medicine like dagnosis. After 3 months medication I again had my ultrasound and this time nothing shown. So she said your endometriosis dissolved and now you are fine. But after 1 month when I have my periods again I experienced severe and strange pain at bottom, back pain with nausea and had vomiting. I experienced same uncounciousness after vomiting then my body temperature go up and started feeling very heat  and sweating and after 15 minutes my body temperature gone down and then feeling very chilled... Such a bad experience every time in my 1st day of period.. if anyone have same experience please share your reason... If ultrasound showing nothing then is there a chance of having endrometriosis