What Causes Delayed Heavy Period With Cramps And Pain In Stomach And Back?

hi sorry to bother you but i m worried as my last period was on 27th dec then yesterday it started very heavily .... my previous cycles were 25 days, 27days, 23 days 28 days and now 31 days this one was unusually late I had alot of cramping the days before it started and pain in my back i also felt sick throughout the day so i thought i maybe pregnant.... but now its come it seems very heavy and i stillhave alot of pain in tummy and back ( i normally have pain but only the first day really and before) ... sorry hope thats making sense