My periods are usually extremely heavy. this month my period was odd. very painful, very light and also extremely painful to sit and when i start to urinate. not pregnant and not urine infection. could it be anything else? or just an odd moment?

Irregular bleeding can be caused by many things, some serious/some not: stress, weight gain/loss, new exercise regimen, lack of sleep, contraceptives, hormonal disruption, uterine fibroids/ endometriosis/ adenomyosis, ovarian cysts. Typically the irregularities last only one or two cycles. If they continue or if the bleeding becomes very heavy, contact your Dr.