Cramping after period??

Has anyone ever cramped 'after' their period? I had my normal 6 day period. Heavy my first 2 days, medium my 3rd day, & light my last 3 days. Now I am off of it and laying here cramping like I am about to start again? I am even cramping within my lower back. The cramps are not caused by sex or chance of implantation from pregnancy, as for I am a virgin. Therefore, what could be the cause for cramping after your period? All opinions are greatly appreciated!