Did you know that I am extremely self-conscious about my size in bed?
What does your size have to do with anything in bed?
I feel like people can tell I'm not a great lover
You are a size that is unusual to you, some people feel awkward when making love in this case. Embrace the real you, and if anyone complains then you have to look elsewhere. People can be replaced all the time if they don't understand you, be more secure about that and you will always win in life no matter what it is about.
That's easy to say when it doesn't involve you.
Trust me, I've been worried about a lot of the same things that you are and it is normal. Judging yourself is sadly one of the most common parts of being a person, and you are not alone in this struggle at all.