12 year old on laxatives

[Carter16]

My ds has from constipation (due to withholding) so every few weeks/months he undergoes a course of laxitives to help clear his bowls so that it doesn't compact. Normally its not too bad but we have left it longer than usual and he is fairly constipated. Because of this yesterday I (regretably), over the course of the day, gave him double his does and it has resulted in him loosing control.
Last night before getting ready for bed they finally kicked in and he was caught short of the toilet. After cleaning up and going to bed he woke me up to say it had happend again. He wets the bed so was warring his 'special pants' at the time (a nappy!) which was helpful.
This has continued on today, he has turned into a pooh machine and was soiling himself every hour or so. ITS SO BAD HE HAS HAD TO SPEND THE DAY IN NAPPIES! Honistly he is so embarrised, his siblings are understanding but still their has been some teasing from his sister. I feel awful, it was on my trust that he took more than he should have. Whilst it is going prevent constipation its still not nice for him. Sometimes his pull ups don't hold it all (they are only meant for bedwetting). He has actually gone threw a whole packet!
Has anyone got any idea on how I can make him feel better/ say sorry. He has had moments when he was younger that were worse than this and its better that getting fecal compaction. But still I feel so sorry for him.
Thanks for reading x