Childs pain please help?

a couple of months ago my son started waking up everymorning with pain in his leg...each morning alternating legs for about 4 or 5 days.severe pain in would start off with but get easier as the morning went. that all went away untill yesterday when he woke up like it again,this time he woke up at 5 in morning to use the loo and felt the pain then and woke me up cry8ing with it.he went strat back to sleep ,i sent him to school knowing he will be ok,this morning its happened again and is in other leg on the groin area,yesterday behind the knee.to tuch it makes it worse .he has doc app tommorrow but what could it be? i thought growuing pains but people have worried me!!