Does your normal face expression look angry or sad for some reason too?

i can be just sitting there and my mom will be like "what's wrong?" and im like "nothing" and then she'll go on this whole thing about how i look sad or angry, but its just a blank expression. then it'll make me angry when someone mentions it because i'll be like "wtf im not angry! i was just talking 3 seconds ago!" or like in the morning my friend said she doesn't like when ppl look sad and bored, and im like " cause we're tired!" and my mom acts like she wants me to walk around with a huge smile on my face like a maniac. is your normal expression the name way? how can i fix it? because this is really annoying me.