Definitley not pregnant and 4 days late?

Hi there,

I hope some one can help me. I am always a regular 28 day cycle girl, my periods are always very very light, just thick brown and will be over in a day and a half, i do get quite bad pain too. I am now 4 days late with very slight lower back cramps and sometimes a tiny bit in the lower stomach, but no sign of period, I havent been sleeping id say past 7 nights have been rubbish and im now feeling tied. I want to start trying for kids in 6 months but I just dont know why i am late, been no more stressed than normal just not been sleeping great, any advice much appreciated, im 29 and have been off the pill 11 months, my first 2 months took a while to get into a regular cycle but then after 2 months it was every 28 days, ive been same weight for past 8 years too, its all a bit odd? x