it dosent sound like you are pregnant to me. The injection is really effective and lasts for 3 months or over - in fact when i stopped it the last one lasted for about 5 months before i had a period. You are supposed to be able to have unprotected sex whilst on it arent you? that's the whole point? and as you had the sex last week when the injection was supposedly still working, i cant see a problem really, as it's just the same as any other time you might have had sex within the last 3 months. When you start the injection it always mucks your periods up anyway