What type of problem is this?

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

Sounds like certain people and situations being out the insecurity in you.

Maybe you only feel confidant on what you deem to be an even playing field or around people you deem inferior...

Whatever the cause, it definitely sound's like insecurity.

Hello Chocopiano27: This sounds like a type of social anxiety to me. But, really, to get an accurate assessment regarding what's going on here it would probably be best if you could spend some time talking this through with a mental health therapist... if such is available to you where you live. Otherwise all you're going to get is opinions (like the one I just gave you) which may or may not be at all relevant. Plus, what's more important here is what you can do about what you're experiencing. And that's something you may well need some professional help with to resolve.