What Causes Abdominal Cramps, Headache And Dizziness?

hi im 18 years old and in the evenings iv been feeling really dizzy, feint and sick? i also keep gettin stomach cramps like period pain but it cant be my period as my last one ended about 2 weeks ago? the other day i also had pain in my back and upper legs? i also keep getting headache, this has been happening for about 3-4 days? why is this?