I've liked very few jobs I've had and keep being let go, despite giving my all. Pls help me avoid a repeat.?

I've done retail work, at which I was very good and got promoted until I had my own store, but felt unfulfilled, so quit and went to secretarial school and college, and then became an admin. asst. to various top execs in the telecom arena (CEO's, CIO's and Presidents), then left that and became a dental assistant/front office manager. Please help me because I'm depressed, demoralized and feel like I can' t take many more new starts in my life. Although I give my best, I seem to be consistently misunderstood and misinterpreted, and I have lost all my joy.