Happy birthday! And FFS, who cares about Facebook? People are making way too huge of a deal out of nothing. Just live your life. Sometimes I post stuff, sometimes I get a lot of replies, sometimes I don't and I notice that others get more replies on their stuff too. Doesn't bother me the slightest bit. I scroll through my wall once in a while and sometimes there is funny or interesting stuff, sometimes not. It's just a thing to do to keep people updated on your life who wouldn't otherwise be in touch, or to catch up with others who are far away, etc.
If you're getting depressed using Facebook you probably have larger issues that need to be addressed. Get off Facebook and go outside, probably will help a lot. Facebook should not be having such a dramatic impact on you.