Is constipation common for kids with Autism?

My 4 yo has never had a "normal" bowel movement in his life! He will go for days w/o anything or just a "smear" in his diaper. Then the sever cramping hits followed by screaming and clenching of his butt cheeks. needless to say this doesnt help.

Our doctor put him on miralax which makes it like pudding/fudge consistency but still no where near a normal amt. This is really hindering potty training.

The doctor suggested trying the metamucil wafers. He had 2/3 in 3 days. nothing. I also have IBS so I tried them 6/day for 2 days. OMG!!!!! Its like cement in my colon. No wonder he is so bad off. he continually screamed help me last night. we tried all the tricks, warm bath, lots of fruit, his special juice, gatorade, including a suppository ...nothing!!!!

Calling Dr. this am.

any suggestions appreciated. Ty: confused: