Thanks for your question. It sounds like you may have had some sort of breakthrough bleeding/spotting. This can happen sometimes midcycle and is very common. Also, If you are sexually active sometimes sex can dislodge any blood that didn't come down with your period. It's not uncommon at all to spot or bleed a little midcycle... always keep an eye on it though, in case it persists and becomes heavy bleeding or if you have other symptoms with it (such as pain).