Women only please.... Needing advice from a nurse...?

I'm not taking any contraceptives. I usually get my cycle every 4 weeks, lasting 5 days max, with no cramping, but maybe moody. Well 2 weeks after my cycle finished, my cycle comes again, and I have had it for 16 days now, with very very painfull cramping on my left side, on my middle and lower back, as well as my rib cage, hip, stomache/lower stomache. Some days it is almost unbearable, and brings tears to my eyes. My stress levels have been minimal, and my environment normal. What is going on?