What Causes Back Pain, Spotting, Abdomen Swelling And Dark Urine?

i am 30 years old woman.i have 2 kids and history of pco's. For almost last one week i am suffering from lower left back pain that moves towards my left limb and i have been spotting continually without a proper menstrual cycle. The colour is brownish red.I have also observed that my lower abdomen has swelled up a little bit. The spotting usually results when i climb the stairs, do driving, or a lot of work. the colour of first urine in the morning is also very dark as if there is blood in it. Kindly guide me what to do and should i be worried...