well i dont know what it is, your muscles might be pulled. switch off with ice and heat and take a hot bath. stretch them a lot to get them loosened up. if they keep hurting then stay off of them so they have time to heal. (unless you have an important track meet coming up) i pulled my hamstring over 4 months ago and it definatelly does better when i lay off of it for awhile. they might not be pulled, but if it doesnt go away then you might want to go see a doctor to figure out what to do about it.