How Can Delayed And Irregular Periods Causing Pain Be Treated?

Finally.hi there.im a 20 yrs young college student.average in height and i weigh 50K.my period has been irregular lately and when i get it early,i hardly feel pain.but now it came 3 days late and im in serious pain.iv been up since 1am nd its now 8:56am.my lower bck hurts the most.what is wrong?