Umbilical hernia

Ok yall. I'm 18 weeks pregnant. I recently noticed that my now outie of a belly button is moving (slow circle motion). I as a first time mother to be became excited. When I told my sister in law she said it might be a hernia (she's a nurse). So during my visit I told my OB and showed her a video but she just shrugged it of. I am now noticing when I lay on my belly the my outie reverts to an innie..it's like a gross magic trick. Is this normal? I hate not understand what's going on with my body! Have anyone experience this?