OK. Like you, I've been quite up and down, in my case by 2 1/2 stone. Doctors disagreed I was overweight even at my peak because I was still below a 25 BMI. For years I've seen MNetters who are six inches shorter and 3 stone heavier than me claim they fit into a 10 when at a taller height and lower weight I wouldn't go below a 16, honestly. But here's the thing: it depends on all sorts of things:
- how tight do you like your clothes? (note this may vary with some times of year -- when it's hot I go looser in clothes)
- what is your shape (ie wider waist, bigger bust, broader shoulders, where does the weight sit?) you may find you're one size on top, one on bottom, you may find some brands work better for your shape, you may adjust some bits. Losing weight may also change your bust size but not your shoulder width or (in my case) your waist by much --
- what brands do you buy? and even within brands -- I still swing from an M & S size 6 to 14, literally this last month. Some of this is top vs bottom half but a lot is just them being very inconsistent in their sizing.
- You can tweak more than you think by having a dry cleaner cut in simple darts, bring up hems, drawing in a waistband on jeans (you can adjust some things more easily than others -- darts, waists, or lengths are easy to adjust at your local dry cleaner, shoulders are a problem, clothing that's lined will be a problem). If you are worth buying clothes, you are worth fitting them this tiny bit to yourself.
Your weight is not about the clothing size. I do think most Brits wear clothes too tight, which is not flattering: you'll look slimmer in slightly looser clothes, just don't go baggy. Brands will have a "standard model" and some will work better for you than others it's them, not you. But also, some the "standard" models might work for your bottom but not your top which is fine until you want a dress, which needs to fit both top and bottom.
In short, as PP have said, no one sees the size inside your clothes (though it does help for you to to keep track by size/brand/item so you know what to try on/buy online next time). What matters is how you feel: do you feel good at this weight? Does it line up with whatever you think is your YOU before (who knows) babies, medication, age, whatever?
Whatever the size in your clothes, you should feel confident in your body. And you should feel good about losing some weight, assuming you're doing this a healthy way.