How can you tell if you're losing weight?

Like
When you work out I know you feel the burn or whatever but I know that's not it

One day you look in the mirror and next thing you know you look different I mean I know That's not it

So like of you feel a burning feeling in your stomach or something while you're not working out does that mean your bodies reacting to you working out or something?

And another thing
Why does my sister keep teasing me about my weight
She's 16 and I try So hard I work out and walk I'm always at the gym and she just keeps messing with me
Like today someone misplaced their food and right in front of me she goes
"Fatass probably ate it"
Or if I'm eating shell be like
"Is it good fatass?"

Why does she do this to me
How can you tell if you're losing weight?
Post Opinion