Glycerine (sp?) suppositories for 1 year old

My son is a year old and has been constipated for  a couple weeks now.  He has been using milk of mag. as per doctors orders (1 tsp twice a day).  The poor child is still constipated and I spoke with a nurse at the doctors office and they told me to give him a glycerine suppository.  My son is in my mother and sisters care during the day while I am working, so my mom went out to the drug store and got some Pedia-lax suppositories.  On the box it says if there is no bowel movement after an hour or rectal bleeding call doc immediatly.  Also says can cause rectal pain and burning.  Has any of you given these to your children and had any of these reactions.  I am questioning if 1 - It is worth putting him through pain, if indeed it does cause pain and 2- giving it to him while I am 30 mins away from him if it doesnt cause a bowel movement with in an hour or rectal bleeding.  Any ideas?