I hat when people disregard my feelings when I complain about how my clothes fit.
Does this have something to do with events in your past?
Yes! Years ago I was ridiculed by that comment from a teacher
People are trying to reassure you that your body is just fine, even if clothes are made too small for real people.  It's rude of you not to take their kind words as a compliment.
I know they are trying to make me feel good but I just can't accept it...
I realize taking a compliment can be difficult for some people but you have to try and remember that you are worthy and it's okay if people let you know that.