No idea if it's the same thing but my cycle became irregular and much shorter in the last year or so. It used to be up to 31 days and has been down to three weeks (I have been tracking it). I was also bleeding lightly mid-cycle (around ovulation time).
I went to the doctors and my GP examined me internally - nothing wrong. Had a smear test, a Clamydia test, blood tests for anaemia and hypothyroidism - all came back negative. Something which can cause this is ovarian cysts but my GP says she does not believe this is so in my case (from her examination).
She felt it could be a delayed hormone imbalance effect (18 mnths later) from my having been pregnant - that I could be perimenopausal (age 39) and/or it could be caused by stress (bereavement, house move) and weight gain/nutritional deficiencies. So, in other words - could be anything but nothing serious and nothing that could not be fixed by healthy-living.
Found out from the smear test that I had a yeast (Candida) overgrowth, although no thrush symptoms. This can indirectly cause problems with hormone balance, (although this was gleaned off the internet, not from my GP). So, I have been avoiding certain foods containing yeast and consuming good bacteria to fight it. I've always had PMT so I am now also taking a herbal complex tablet containing Agnus Castus and Motherwort. Agnus Castus is supposed to help balance the production of hormones by the pituitary gland. It takes about 3 months of continual use to get the full effect.
Anyway, hope all the above is not TMI, and not too boring, but my cycle does seem to be settling down and averaging about 25 days now. The mid-cycle bleeding has stopped and the PMT is becoming less of a problem. I would prefer it if the cycle were longer but at least it is fairly regular.
I wouldn't worry too much about it but I would go and see your GP in the first instance to rule out anything serious.