For a shy person you're sure bold over a keyboard... you posted a thought on the internet asking for feedback, so you have to accept that of the millions of users on reddit, someone was bound to respond with something you didn't want to hear.

Why not ask a question someone can actually provide a useful answer to? Why do you feel like you aren't good at your job? What kind of mistakes have you been making? If you gave details maybe someone could actually give you specific tips to improve... all you've said is that you feel like you suck at your job, even though you haven't received that feedback from anyone at work.

If you really want guidance, give people something to work with, but with the information you've provided all anyone can really say is "have confidence in yourself" which makes it feel like an attention grab.