Bad at Contributing to Conversation

Ugh! Why must I be so bad at contributing to conversation? Seriously, it's very annoying. I've been talking with this guy he's actually my brother-in-law's friend on Facebook for months and our conversations never last long. He'll say something and I won't know how to respond to it. It sucks because I really enjoy talking with him. And I'm blaming this on my shyness. It doesn't just happen with him, it happens with almost everyone I try to talk to irl or online. I hate it. I just want to have a nice conversation with someone for once without me taking an hour to think of something to respond with. He just told me he woke up and he's working overnights now. I don't know what to say to that. And this post probably doesn't even make sense. I just felt like ranting. Sorry about that. But I seriously do hate not knowing how to contribute to conversation. He knows I read his message. He's waiting for my response. I want to give him one, but I honestly don't know what to say. He probably thinks I'm deliberately ignoring his message. I'm not. I'm gonna go before I start repeating myself.