I am on the implanon, i had a period about 2 weeks ago. yesterday i began having severe cramping in my stomach, radiating to my back. suddenly bleedin?

Not likely: Iud's are one of the most effective forms of birth control. Irregular or absent periods are an expected side effect. Failure rates are 1%. Anytime you suspect pregnancy take a home pregnancy test. They are cheap, reliable and available at any pharmacy. If your test is positive you should see your doctor urgently because of the risk of tubal pregnancy (ectopic pregnancy).