Hi Shy Introvert. I understand, it happens often also to me not to feel comfortable in groups. And it happens also to me (expecially it happened when I used to go to parties with many people...now I practically stopped) that I think to behave 'normally', but people don't seem interested in interacting with me. My idea is, like you said, that maybe our discomfort is visible though we try to hide it, and this doesn't encourage people to talk to us. I don't know. In this case, maybe you just need time to feel more comfortable in that group, and then you'll become to appear more natural and things will change.
At least you kept in contact with one lady. You could try to know better other people through her.
Hope that you feel more comfortable soon. I know that it's not pleasant to have to struggle to find something to say when everyone else seem to be having fun