Why aren’t my coworkers being friendly to me anymore?

For example, they don’t really reciprocate conversation when I say hello or how’s ya week been and that, and they don’t ask about me as well, only a hello and that’s it.

They’ve also been avoiding and ignoring me. I try to talk to them and say someone but they don’t listen and look at me with a weird smile. We usually sit together as a group, buy while waiting for them at come, I looked behind me and saw them eating together at a completely different table, not even asking me to sit them either.

I don’t know if it’s them or me? Because of the way they’re behaving towards me, I’ve started to be rude back.