All of a sudden not pooping

All of a sudden toddler won't poop

Not even sure if this is the right spot to post but my daughter is almost 4...has been potty trained (pee, poos during the day and night time), since she was 1.5 years old. All of a sudden, she is holding in her poop. She says she is scared to poop b/c it is painful, so she has constipation.

Since I've called her pediatrician, she drinks 1/2 cup to 1 cup prune juice a day, I've been giving her PediaLax to also soften, intake of fiber is also great. But she literally holds it in on purpose. She is also eating 3 meals a day + multiple snacks throughout the day.

We both watched toddler friendly poop educational videos...endless hours of it, given her positive reassurance throughout the days. Its been almost 3 weeks now.

How else can I convince her to poop? She completely refuses to sit on her potty to poop too. I’m at my wits end trying to think of things.

It’s been over 2 months and she’s just holding it in on purpose now. She gets the natural daily urge to poop but just cries and cries until the poop feeling goes away. The consultation is completely gone because when she does poop, she doesn’t cry during the actual poop. It’s solid brown and normal/healthy poop.

Update #1:

When this first started, over 2 months ago. It was once a week.

Since the last week of March it’s been every 3-4 days.

She has urges to go because of the prune juice and me changing her diet and doing more fiber.