I'm sure you DON'T look horrible, but I know the feeling.
In our mind's eye we are still twenty as far as looks go, or whatever age we think we looked best at. Then we look in the mirror and see an old woman with thinning hair, bags under her eyes and lines on her face. This is a word picture of ME. And we think, "Who is this old fright?"
You're on a diet, full marks for resolution, don't overdo it though, will you.
Finding clothes that look nice on women our age is a pain, as nothing in the shops looks good - they only cater for 17+ girls. Hope you find something nice to cheer you up in the nearest charity shop - the prices are right there!