My facial expression is not matching my words

The other night, I realized that sometimes my words don’t match my facial expressions. The only reason that I know this is because my boyfriend and I were talking about something and I responded by shaking my head yes. Shortly after that, I said no. He was totally confused by this, so he asked me what I meant. Then he explained why he was confused. He told me that I shook my head yes and I thought I had shaken it no. I am hoping that this isn’t a new problem, but if it is, we will just adjust and find a way to deal with it. Communication is so important in relationships, so we will continue to make changes as needed.