Welcome. First you should not put any more negative thoughts for your self. I have been there and analyze it too much to find a solution. If you feel you suck at your job could be one of the following reasons.
Monthly payment is not enough.
If your monthly payment is not enough, many people react bad in the tough economic years we are passing through, and this could affect you psychology and then the work you are doing. If you are unhappy with your work environment this also could affect the quality of work you are putting.
People behaviour is bad.
If you are treated bad or people at work are yelling at you, could be a very good reason not to love the job you are doing. Consider speaking with those people if you find it appropriate. If you are thinking leaving this job start building a plan to exit this job.