Is there anyone else who experience the things I feel, and is there any specific name for that experience?

So I'm usually confident and carefree as a girl, but when I'm around a group of popular people particularly popular girls, I become so quite, distant, rude, unable to say anything. I'm not usually very serious, but my fun and loud personality just disappears in some situations and I'm unable to understand why, even though they treat me nicely it still terrifies for me.

I'm not my usual self in some situations, and I'm unable to change back to the real me, at least not until I feel comfortable with myself again (which is also very hard for me). It's really hard for me to say no, and point out the wrong things they do to me, I usually just keep silent and let them do whatever I want and say to me. But sometimes it's just too much, but even though I'm loud I'm afraid that my words will hurt them and so i choose to keep silent.

Why am i like that? And why can't i be myself around some people / situations. It's effecting my life and makes me worry to much, it's so tiring