it's getting worse

About 3 weeks after my second son was born, my first son (he'll be 3 in November) started pooping his pants every single day. We had previously been accident free for a long time. At least 6months. Like, zero accidents. ZERO. And now, he hasn't had a single poop for 3 weeks that was I his potty. They've all been in his undies. Well I was told by a couple people to just ignore it and it'll stop. So I clean him up but try not to make a deal about it. Well tonight, after he had already pooped his pants once today, my husband walks in on him squatting and pooping on the floor right next to my side of the bed. What is this? My husband is not very patient at all with him and immediately flips out like every other time he poops himself. I have to remove him from the situation, but I have to admit I am becoming extremely frustrated myself. I have no idea what to do. He was extremely easy to potty train the first time. We just put him in regular undies one day, had a few accidents but then that was that. Please, has anybody else gone through this?! Please answer because I got no responses the last time I posted this and now it's only getting worse. Am I not paying enough attention to him since his brother was born?