I feel so dumb for caring about this

A couple weeks ago I found out a coworker twice my age is saying I complain to much and see I would understand if I did but I don’t think I do I barely even talk at work unless it’s to specific people and we are joking around. What’s even worse is I used to babysit for her and when I had to leave because my job wanted me to work more I volunteered my sister to be my replacement well I found out she’s been saying stuff about me to HER to. I obviously was extremely hurt because I mean I don’t even really talk to her and it never feels good to hear bad things about yourself.