Kind of a question more of showing off

Can't believe my son will be 4 this Saturday. He's father passed away when I was 5 months pregnant. Just dreading the day when he starts asking questions. I know he's watching over us though. I actually have a question though. He still isnt potty trained. Ive tried everything. Giving prizes when he goes, putting underwear on him, making him go every so often. It's really rare when he actually tells me when he has to go and its mainly when I tell him to do something like clean up toys. He'll say he has to go potty just to stall.