Extreme poop problems

My daughter is almost 4 and is pretty well potty trained when it comes to peeing, but pooping, not unlike most kids, has become a huge issue. However, Not only is she refusing to poop in the potty, but she refuses to poop at all. It started this past summer and she was just getting constipated really easily. She would go a week at a time without pooping until it would just all come out and it would hurt her really bad.

Since then I’m pretty sure she’s started holding it because she’s scared it’ll hurt, but it’s getting to the point to where liquid is coming out around the hard stuff and burning her and causing her to get infections. We’ve met with the pediatrician a couple of times and we’ve tried changing her diet, her milk, giving her probiotics and fiber supplements, we’ve had to do suppositories, but it keeps happening and she’s really suffering. We’ve had to take her to the ER once and went to urgent care a couple weeks ago because she got a bad infection. She pooped while we were there and the doctor said that something that big should not be coming out of an almost 4 year old. It’s just insane.

We have an appointment with a GI specialist in January (that’s the earliest they could get us in), but until then I have no idea what to do. It’s now getting to where she’s having multiple pee/bile accidents in her underwear a day, the infection is coming back, we can’t get a suppository in her because she fights us so hard trying to do it that we can’t hold her still and I’m afraid we’ll hurt her because of all the struggling. We’ve tried bribing with candy, toys, sticker chart, “poop fairy,” anything you can think of. I’m at a completely loss and I hate seeing my baby in so much pain. If anyone can offer any kind of advice it would be greatly appreciated.