Difference between muscle "burn" and muscle injury?!

ALS_1980

So I have to be careful when I workout because of a previous accident. I want to know how to tell the difference between good muscle "burn" and muscle pain/overexertion. My ankles and knees hurt a lot after working out usually after I've been at it 10 or 15 minutes. I was told by another gym patron that at my size it's going to be the case until I lose a considerable amount of weight. Someone else told me that soreness is common but pain is never good. How do I know when I'm pushing it?