scout79,
Pain under a splint or cast can always signal a problem. If the pain is not relieved with elevation, then you should contact your surgeon and ask to come in early.
Try elevating the limb so that there is no pressure on the point of the heel. This is always a pressure area in casts. Place the leg on pillows or pads so that the broad area of the calf is on the pillows, and the point of the heel is hanging free.
But, if this does not make the discomfort a lot better, contact the surgeon's office and state that you need to come in early, because you are having a significant cast problem.
No surgeon (or their staff) should ever just disregard a patient complaining of cast problems. There is no excuse if a patient develops a cast sore after informing the surgeon that they are having a problem with the cast. Of course, the patient is responsible for proper care of the cast, not sticking anything down the cast, and for not resting the cast on the pressure areas.
Again, if the cast is still hurting, call the surgeon.
Good luck.