Hi OP
I too feel this way about myself. I work in an incredibly caring role, and will always go out of my remit to help someone. I have also done this most of my personal life too, a perpetual people pleaser. I have been consistently taken advantage of, I have scaled so much back. I never ever feel good enough.
I tick all the 'low self esteem' test boxes, and I'm very insecure. If you met me or asked people who knew me (not really close people) they would say I'm confident and quite possibly gregarious, also been described as vivacious! Certainly not a wallflower. There is part of me who is that person, then I will recount all of my gregarious/confident conversations and pick them over with a fine tooth comb
I constantly compare myself, I'm never good enough, I don't begrudge people having 'stuff' good luck to them, but I would like some for myself, I'm sure that's what most people do.
I can 'gossip' and I've said some horrible stuff over the years, and it's all because of the way I feel about myself, so I kind of feel exonerated!
Have you looked at the 'inner child' work OP? A lot of this stems from childhood, it might be worth looking into.
Lastly, if you weren't a nice person, you wouldn't be here acknowledging your problems, so take comfort in that