Potty training failing each time.

My son is gonna be 3 in august, I’m getting shamed by anyone around me for not being able to potty train. We’ve been trying for 3 days now but when he see’s the potty or toilet, he we scream bloody murder until I put a nappy back on him. Today he sat on the potty for almost 15 minutes, as soon as ne got up and I put his knickers on, he pee’d. I said it was okay and tried sitting him back on the potty, but he just kept screaming. I also have a 1.5 year old girl she is the same. I feel like I’m moments to giving up and bursting into tears to think what I’m doing wrong when everyone is able to potty train 😭 Any advice for this weak and depressed mama 😭