My 6 year old was prescribed singular for allergy relief. After ...

My 6 year old was prescribed singular for allergy relief. After 1 night of taking it he woke up with leg pain. Not too severe, just sore so I thought they were just growing pains. After the 2nd night of the medicine he woke up and his legs hurt so badly that he has a very difficult time walking. We took him off the medice. After the 3rd night with no medication he woke up with a little leg pain, but not anything like the previous day. After the 4th night he was fine and has been fine every since. It had to be the singular. My pediatrician did not have any other children that had had this type of reaction, but said that we should not give it to him again. He said that we should listen to our bodies, and if we don't feel right after medication then we should stop taking it. It was scary for my little boy