What Causes Severe Abnormal Pain During Periods?

1 month ago i went to the emergency room cause of my period,it was very painful and i even puke.
they sent me home and 1 week after that i was bleeding again,and having pain.its been a month and it hurts in my left side of the abdomen,ovaries and my lower back. i have been with 2 gynecologists and they told me i have no infection like 3 times.All negative. 1 week ago i started going to the bathroom so many times. they can't tell me what i have.... what do you think it could be?