Thank you for your query.
I hope there is no reason to worry. few details are needed before coming to a conclusion. does you child have head control,does you child's neck and body feel very lax, what is the weight of your child,does he look abnormal in any way. the other milestones you have mentioned are normal for his age. If the child feels very lax and has a abnormal facies it might be case a down's syndrome which is usually associated with hirschsprungs.If your baby is very lethargic a thyroid
function test may be done.Do not panic.If the problem persists consult your doctor.Have a nice day