Girls, hello, yesterday my belly was moving like it had a life of its …

Girls, hello, yesterday my belly was moving like it had a life of its own, even hurting, there's some movement today but not very strong. Is this normal for a baby too? Every day their mood changes like mine (my doctor said so), or is it something else? Could it be that the baby rolled over upside down and feels weaker because of that? It might be a strange question, but I'm having my first pregnancy, I still don't know much about everything!