I need serious potty training advice

My daughter just turned three. She showed interest in using the potty to pee around 18 months old. Peeing on the potty was going pretty well so she was wearing underwear most of the time. She refuses to go poop on the potty so extreme that she will hold her poop for days and literally make herself sick. Our pediatrician advised to just put her back in diapers until she is ready so we did. We keep going back and forth between diapers and underwear every few months based on her cues but the pooping on the potty is not getting better. When she poops in her diaper she hides in another room, she screams and cries if you interrupt her and screams and fights the entire time you change her diaper. She seems to have some serious emotional issues connected to pooping. We have tried everything we can think of and nothing is helping her get over this issue. The doctor has also ruled out any medical issue.

Any advice?

Moms Expertise
    But even pooping in the diaper has become a huge issue.

    We have tried candy, ice cream, fries, etc. We have tried every positive reward we can think of.
      Margaret hernandez
      18m is a great age to start potty training. always ask them. do you have to go pee pee. even when they say no you should take them to the potty this is ware we go potty at. sit on the potty see this is how mommy does it, know you try. make a BIGGG deal when they do just set on the potty. in a good way. yaa you did it. do a potty song and dance lol.now one will see you... getting them to pee is the easy-es..getting them to poopie will take a little longer about when they are 2.5 years old they might poo in the potty are soon..just dont give up it will happen...
      Comment deleted
      She will hold it for day, making herself sick. She got really constipated and needed medication. She was having tummy aches too.
        I trained all my three kids to use the potty - designed and made by their grandfather (my husband side) who was a carpenter. This thing both used as peeing and pooping. For my first child about to turn a year old I first showed it to her describing how beautiful that chair type (potty) especially made for her by grandpa. I had to make stories/bluffs...and played with her a little bit...then afterwards I said "do you want to try and sit down on this nice chair?" I did that every morning to her and sometimes in the afternoon. I would always ask or remind her that to tell Mommy if you want to use it okay. She learned quickly and my other two children were the same - very good followers.
        About Katie
        Birth: November 24
        On Moms.com since: Jan 21, 2014
        ***Community Manager of Moms.com*** Mom to four amazing children. I am passionate about helping and supporting new moms as they enter into motherhood. I am a certified doula, certified childbirth educator and an accredited breastfeeding counselor.