Ok what's wrong with my

Here are my symptoms- I was 6 days late starting. All negative preg tests.  Started my cycle and on day4 of my period started getting really bad cramps and abdominal pain and slight constipation like i had a year ago (not during period) that went to the er and they had said I had fee fluid behind my uterus likely from a cyst rupturing (that time I had a fever).  This time everything is similar except for no major fever - maybe a low grade. I took a preg test yesterday (negative) going on day 4 of this pain on my right side in front and center all low bladder and uterus area.    Cm has been bits that are almost like lining shedding and dryish ( not sure if from this or ending my period ). What's your thoughts?  Should I go to er for an ultra sound? Wait it out more?? They likely won't do anything other than blood work and an ultra sound