Third ultrasound

I’m currently 24 weeks and today I’m having another ultrasound recommended by my doctor. He had said they couldn’t see anything clearly since baby wouldn’t move at my 20 week scan. Should I be worried? I didn’t think about it until now but I’m scared there’s something they aren’t telling me. Has this happened to anyone else and it just be another scan because baby was in the way? Or are third ultrasounds usually a bad sign?