The implanon is a great little contraceptive method but unfortunately one of the side effects can be troublesome bleeding. Some people can just spot unpredictably and some can just bleed for long periods at a time. Blood that gets old looks brown, so I wouldn't be too worried about the colour. Your doctor is right about your 'ninja day'-that is entirely normal. In terms of pain during sex, see your GP. There are many causes and depending on whether the pain is superficial or deep, the causes can differ.