My friends make me feel uncomfortable and left out?

So I have these two friends. I'm very close with both of them. But they are best friends. Whenever we are hanging out, they only talk to each other. They do a lot of PDA, and that get all gushy. They have all these secrets that they talk and brag about to everyone but would never share. It's uncomfortable and angers and upsets me! I've told them before, but they didn't do anything. They'll be sitting across from me at lunch doing this and I'll just have to awkwardly feel left out and avert my gaze. And in German, one sits behind me and the other sits next to me and they always hold hands and pass notes behind me. I think it's very rude and disrespectful of them. And no, they're not dating. Advice? No rude/ inappropriate comments.