Is it normal for my boobs to be rock hard with what feels like muscle spasms every time I get up from sitting? (5 days post op)

Dear Samflor13,I understand your concern and it is quite normal to be concerned about the outcome following a breast augmentation surgery. However, you are still in the very early stages of the healing process at 5 days  post op.Your will need to be patient at this moment and follow what your surgeon has instructed you to do post operatively.At the early stage of the healing process, the tissues around the implants are still swollen. Once the swelling subsides and the implants drop to their final position, you will be able to see the final result of your breast augmentation surgery.Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

At 5 day you are about 3 percent soft, healed, settled, shaped, dropped and fluffed. "Drop and fluff" refers to the fact that as the skin stretches and the muscles relax, the implants move down and out slowly – about 1 percent a day. It’ll be about six weeks before they even begin to settle down, but they’ll be close to 80 percent settled and softened at three months. Watching their progress is like watching your hair grow. You don’t see a difference in your hair growth daily, but all of a sudden you need a haircut. 
Be patient after surgery. Give yourself a few months before making a judgment about your surgical results. You won't know the outcome until then. 
Dr. Ted Eisenberg, Board Certified Plastic Surgeon and Author

Hello dear!!
Thanks for your question and provided information.
You are still early on healing process. It is normal to feel stiff, and you can expect to see your final results after 6 months. 
Please, be patient, but if the situation doesn't improve over time, I suggest you to follow up close with your plastic surgeon.
Hope this is helpful. Good luck :)