Sa 33 weeks, dark brown discharge pwedeng normal sometimes, usually old blood lang na naglalabas, pero honestly, better check with your OB agad para sure, lalo na kung may associated pain or if it's heavy, kasi di ko gusto mag-assume sa ganitong stage ng pregnancy. A few of my mum friends experienced this din, pero iba-iba ang reasons, from cervical irritation to something more serious, kaya talaga ang best thing is kumuha ng peace of mind from your doctor rather than worry, you know?