To feel unhappy with being a uk size 12?

[lazysloth]

First of all this is not intended to be 'fat shaming' in any way. I know lots of ladies who look fabulous (and most importantly feel it) in larger sizes.
In my late teens and early-mid twenties I was always a slight size ten (not small enough to feel comfortable in an 8 but more like a size 9). I feel comfortable, happy, confident and healthy at this size.
I am now late 20s and seemingly out of nowhere I am a size 12, bordering on a 14. I tried on some size 12 jeans today in River Island and whilst they fit they really did not look any good!
I am not eating any more or doing any less excercise. Do you have to try harder at this stuff once you hit late twenties/ early 30's? I am really not happy with my body and feel like I need to cover up .
Everyone else says I look fine and this is a normal and healthy size.I am wondering if I shouldn't be so worried about it and it's all in my head? But I'm feeling like I need to go on some sort of diet. I've never been able to diet properly ever and I really hate the gym.

To the person who was asking about clothes sizing in the past, in the 70's (when I was a teenager) most fashionable clothhes were sold in a 10, 12 or 14, and nearly all young women fitted into these sizes. The odd shop sold an 8. If you didn't fit into these sizes you had to buy large childrens sizes (if very small), 'old lady' clothes ie crimpilene if you were big, or alter or sew your own clothes. Oh, and clothes tended to be small on the waist because it was assumed that all women had a standard hourglass shape. That was your choice and it was good incentive to stay slim.

Noeffingidea I remember being a size 8 in early 2000’s and being thrilled to find topshop actually stocked size 8 trousers and jeans, so they must have been unusual even as late as that.