@notanotherottenotter
I’m 8 and a half stone from 11 and a half, and my BMI is about 21. So not underweight, I hope.
I am going to go against the grain here.
Don't know your height, but if you are an average height for a woman, you are at the very low end of a healthy weight and BMI.
I have been up to 13 stone, and down to 8 and a half (I am 5 ft 5,) and frankly, I don't look great at 8 and a half stone... I look gaunt and pale, and definitely look better at around 10 stone. I don't care WHAT the 'weight charts' and BMI charts say, I look WAY better at 10 stone, than 8 and a half stone.
At 13 stone I do look fat though (and AM fat at that weight!)
But yeah I agree that ANY comments about anyone's body size and shape is out of order, but that's people for you. They will comment! If it is thinner people saying it, then it's not jealousy. Maybe they do think you look ill. The weight and BMI you describe, for an adult woman (near middle age,) who has had children, sounds too low.. And if you have dropped 3 stone, and were only just over 11 stone to begin with, I'm sorry, but you probably do look gaunt.
I know some women who are middle aged who have ALWAYS been slim - 9 stone-ish, and they look great, but they have never had any great weight loss, as they've always been slim. When someone loses 3 stone or more in middle age, they often look a bit gaunt. Especially if it has come off quickly.
My DH was 16 stone for a few years, (he is 5 ft 10,) and around 5 years ago, he went on a silly crash diet, and dropped to 11 stone, in 4 months ... FIVE STONE weight loss in four months!! He looked AWFUL. He looked better at 16 stone! He looked pale and gaunt and ill, and his clothes hung off him, even though he bought smaller sizes. He also looked 10 years older. A friend of ours asked if he was dying. 
He regained some over about a year (went up to 13 and a half stone,) and looked WAY better. He has stayed around that weight since...
I have also seen several other people I know (female friends) who dropped 4-5 stone at 40-45, (they dropped to about 8 to 9 stone,) and it aged them terribly. As I said, if you have always been that size and weight that is one thing, but to have always been a bit chubby, and then to suddenly become thin is rather ageing for many....
But I agree that thin-shaming is a thing, and it's unacceptable. I think fat people get bullied way MORE than thin people, but thin people do get rude comments yeah... I also get sick of the 'men don't wanna sleep with a bag of bones' and 'men prefer curvy women' type comments that I see on the internet, as it is bloody rude. And the 'real women have curves' thing REALLY fucks me off. 
Some women call themselves 'curvy' when they are just obese! Curvy is Shakira or J-Lo; not someone who is a size 26, and weighs 20 stone. I am not fat-shaming, but I get sick of obesity being celebrated......