L.,
I completely understand what your going through. My son being only 2 1/2 years old, He's barely understanding the whole potty training so that has been put off for a bit due to him being constipated bad, this is the 2nd time he's been so bad that we have to actually clean him out again. It's a 9 day process and I feel for the little guy, he's holding his poop, (this time around he goes every 2 days but it's a lot that comes out) and he had a yeast infection on his butt a few weeks ago which is gone now. I thought he was holding due to that hurting but that wasn't the case. I saw a GI dr. yesterday and she said it's common for children to hold their poop and that we have to clean them out and then make them regular so they know it doesn't hurt and then back to normal poops then start getting him to poop on the toliet. I know you feel since his age he should be going on the toliet, but you have to pick a battle to beat 1st and the one I think that's important is to get him cleaned out and back to a normal bowel movement.
I found out today after yersterday's blood work that my son is extremely anemic as well, OH MAN talk about constipation now, Iron is suppose to constipate you.
So the dr. recommended the following to clean him out, not sure if your GI did the same
Day 1 Childs fleet enema
Day 2 1/2 Suppository (Durculux, Spelling is probably wrong, but I know they cost more than normal suppositories)
Day 3 17 grams of Miralax
Repeat that for 9 days, then after that is done if no poop for 2 days another 1/2 suppository and continue the miralax to get him regular daily
And she had me give him soy milk now because of being anemic.
The GI dr. also mentioned the sticker chart as well and I have started rewarding him everytime he poops (yes in his diaper) only because I want him to know it's ok for him to poop.
Go to a dollar store and buy a bunch of little toys and have a little special box with different items in there for each time he poops, and once he starts realizing that it's a good thing then you can move onto the toliet.
Even make toliet time fun, go in with him read a book with him, make it a routine before his bath. (I don't know if it will work, but a co-worker told me she did this with her son that had the same issues with her son)
So just wanted to let you know your not alone. I was feeling like such a bad mom finding out my son is anemic, UGh but the dr. made me comfortable by saying it's so common and it happens, so it will get better.
Also I heard alot about Chirorpractor's helping, I started bring my 2 1/2 year old to one that deals with children really well, and my son even said 'the lady helped my back."
I hear it helps align their hips and maybe helps with constipation. Worth a try if you believe in Chirorpractor's some people don't.
Best of luck to you.......
Let us know an update....