"Need to have more confidence..."

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This was the only negative thing on my yearly job assessment. Sounds pretty easy to change right...but I've been working on this FOREVER. I even listen to subliminal messages during the day at work lol. I've been working hard to gain confidence in my social life as well, joining a meetup group and throwing myself into activities and going BY MYSELF! I even force myself through the awkwardness of not knowing anyone when I didn't hit it off with some people, but eventually warmed myself up to the crowd. I'm trying, but still having lots of trouble all-around lol.

Anyone read any books that helped gain confidence? Or helped with anxiety in work/social situations? I always wish that one day I'll have that spark or charisma that makes people feel comfortable around me and want to get to know me, but I think at this point I have too much pent up anxiety that is keeping people away haha.

Thanks for any suggestions :)