Hi,
I have had the same problem with my daughter, she's going to be 4 in July. I ended up telling her that she makes potty and poop and it is her responsibility to put it into the potty now that she's a big girl. Then she just wore big girl undies and I tried to keep her in dresses so if she got her undies wet, most likely the dress would be ok. This took a week or two, she'd wet her undies then stop, then want to go to the potty either because she didn't like the wet feeling or because she was learning the feelings connected with the pottying. SO, we had lots of undies.
She did great after she got the hang of it. But then here we are moving and she is going back to having accidents. She's ok sometimes, but I think the stress just gets to them. She's really worried that we're mad or disappointed when she had accidents, she doesn't mean to. I keep encouraging her because I know she can do it.
Also, my daughter was taking the move rather hard. I kept trying to get her excited about preschool and we'll have some neighbors her age, but then after a bit she didn't want that either. I found out, through other parents that are moving too, that she didn't know all her toy's, clothes, bed, whatever were going with us when we move. We talked about that and everything else we are taking with us and what is not going (the walls, the floor the bathtub) WOW what a difference. She's getting excited or ok with it now. We try not to talk much about who/what we are moving away from. We just say we are sad to leave, too, but we're excited about the new place and we will write/talk to/see our friends and neighbors. It's exciting to get mail. Anyway, that's helped us and our daughter. Hope that helps a little, good luck!