My girlfriend makes me feel like the third wheel?

[toby]

So me and my girlfriend have been going out for almost 3 weeks now, not too long, I know. But we've really connected during these three weeks.
She hit me up on social media over winter break, we started texting a bit and when school started I decided to ask her if she wanted to hang out. After about 3 of these "dates" I went in for the kiss, she denied it and walked off only to text me saying she wanted me to ask her out.
So I did, and it's been great, until we started hanging out with friends.
There's just always this awkward aura in the air, and I don't talk a lot. She, on the other hand, does talk a lot, but not with me.
It results in me feeling awkward, and the friend usually comes to me asking if we're okay. Later on I usually ask my girlfriend, who then replies that she didn't know, and then starts feeling bad about the whole thing.
For me right now, it's just this bad gut feelings about the whole thing, when we're alone I feel amazing, I know she does too. But whenever we hang out with a mutual friend, I want to break up with her straight away.
What do I do?

ps, yesterday when we were texting, she asked about some girl that was snapchatting me, and I replied that it was just a friend and she shouldn't worry about it. She replied with a simple "K." and we haven't texted since.