I can't interact with people

8 months ago, my friends started ignoring me, till now. I was never a social person, but my friends gave me the smallest ounce of confidence. Now, 8 months from then I've been alone. There's specific people that treat me well, because they've realised this. But, whenever we have a conversation, it's extremely one-sided. I can't reply to jokes, and sometimes it's hard to be polite. They can't see my expressions too, so I feel like an asshole. A simple greeting by a classmate can make my day, and I feel like I'll never be able to fix this. Since I can't, I'm ranting.