I started my periods just after my 11th birthday and up until DD3 (4th child) they had always been the same, always on time every 28 days, dull ache in low stomach on the day before period started and day I came off, no pain during, period lasted 5 days 1st day light, day 2 and 3 were heavy, day 4 was light and day 5 was brown discharge
Since DD3 (16months ago) my periods are more like 5-6 weeks apart I never know when they are coming as I don't get my warning cramps the day before anymore and they are heavy from the start with small blood clots and the pain....
The pain seems to be getting worse with each period, I came on yesterday (thanks mother nature for spoiling my valentines night alone with DP 
) and have had a constant dull ache in my lower back, my bum and low in the stomach.
I've also been getting sharp stabbing pains in my vagina like someone has just stabbed right up me with a red hot knife, they are crippling and last less than a minute but then the ache in my bum hurts for a good 5 minutes.
Last year I went on the pill to help with my periods and they stopped them completely...I loved it but after a few weeks I started getting headaches everyday so I stopped taking them after 4 months.