Weight gain

I was wondering if someone could help, I’m 19, almost 20. And noticed that recently I’ve gained weight, looking at myself I don’t look that much bigger, but I don’t fit into most of my old dresses or skirts anymore. It’s so stupid but I’m comparing myself to when I was 17. I’ve always struggled with body image and this has really thrown me. Worst part is I’m not sure why I’m gaining the weight, is it just my age? Im not eating badly and if anything eating less. I’m just so confused and don’t know who to talk to x