Self-depracation is okay now and then, but too do it all the time, I think you might of been using jokes to try and cover self esteem.

Comedian's use it at the start of shows so can relate to audience that a human being and not above them cause on the stage.

I used to do it because I was on the cocky side of things.

I've never done it for sympathy.

If you picked it up from someone, maybe their why the low self esteem.
If you're nervous about something yeah, but if don't address whatever nervous about, and keep joking, gonna get obsessed with problem, but self esteem wouldn't of be high any way if was over doing it.

Watch some comedians on stage (youtube or something) might help.