If it's a dull pain that sort of feels like a bruise, it is most likely just sore muscles. If it's a sharp searing pain that feels like a knife is going into your skin, then it's most likely an injury and you need to go get it properly checked out by a doctor.
Have a hot bath tonight to help loosen up the tight muscles.
If the pain doesn't go away in a few days, book an appointment with your doctor and get it properly checked out.