Child 3 nearly 4 wont poo in toilet

Hi,

my 3 year old boy, (4 in late feb) will not do his business in the toilet. We know it doesn't hurt him, he just wont do it in the jacks ! he'll run under a table, or into a corner, and look as guilty as sin !! Ill ask him is he pooing, he'll say no. Ill put him on the toilet, and he'll hold it for as long as he sitting on it.... He once held his poo for 5 days, and we had to bring him to a doctor for laxatives...

He has mastered the wee's, no problems there, will go of his own accord, and rarely wet's the bed.

We've tried everything for nearly a year now, bribes, rewards, all the encouragement he needs, we don't scold him for not doing it in the toilet. He goes to a crèche, they have been very good and understanding and have tried their best also. But they now reckon our last option is go see a child psychologist.....

has anybody had experience in this,

Thanks