Thank you for your query.
Smecta can cause development or worsening of constipation
. By your description it appears that your son has developed constipation and some stool is passing around the hard stool which is causing pain. I suggest that you get him examined rectally so that if any hard stool is there it can be digitally removed or he may be prescribed some suppository to relieve the impacted stool.
I hope I have answered your query to your satisfaction.
Wishing your son an early recovery.
Rajiv K Khandelwal