Potty Training

Back in August my daughter was 2.5. I did the three day potty training method. My daughter did pretty well with it. She held her poop it in seemed and got constipated and she had some issues for a few weeks but it seemed ok. It was never perfect though. I always had to stay on top of taking her potty .. she never would just go on her own. She will poop her pants now all the time. She will be three in March and I just don’t know what to do. She does have a sister in diapers who just turned one so I think that may attributing to it. She just keeps having accidents and not even telling me. Did anyone go through this? I have no idea what to do anymore. I keep pushing the issue but I’m ready to give up. I’ve been harsh, nice, laid back, frustarted, I’ve been everything and nothing is helping .