What Causes Late Periods, Headache And Lower Back Pain?

I am a 21year old female almost two weeks late on my period, I had bad headaches three weeks in a row and my lower back has been hurting so much. I have been eating a bit more and I feel ive gained weight but now when I eat something and I get grossed out my breast feel with some pain but not super sore and when I lay on my stomach its an unpleasent feeling. I felt some light cramping but no period.