Anyone feeling that?

Hi everyone, i am 26+3 pregnant with twins, and I have been feeling that my tummy gets super tight and hard at times throughout the day and that babies become like a rock inside, like I can feel their heads clearly. Is that normal? I asked my doctor and he said as long as it is not painful that’s normal and it’s not painful, it’s just uncomfortable. Is it happening to anyone else? I am a first time mom and literally panicking over everything so could use your experiences to ease my mind☺️