Potty training sucks

OK so it 10pm and I'm walking around the house shutting all the light off when i smell something. Like a shitty diaper but i cant find it and no the trash does not need taken out. So I'm checking and I come to Stella and that is where it is coming from. After she went to sleep she shit in her pull up. I am thinking "Damn It" not i have to change her while she is sleeping. Keep in mine that she just turn 3 and we are not potty trained yet. She has no interest in it. We were doing great about 2 months ago and it just fell apart. I am so tired of buying diapers for 2 kids and changing double diapers. Anyone with any ideas please help unless your willing to change shitty diapers then come on over.