Okay, this idea will sound kind of stupid, so keep an open mind. I've had the same problem before, with a knot in my upper back that refuses to relax for a few days. Take a tennis ball or something similar and place it under your back while laying on the floor, then move your body until the ball is directly under the knot. Then move yourself around, massaging the sore spot until it feels a bit better.
It worked like a charm for me, and I have my dog to thank for it. I was always amused by the way the big mutt would roll around on her favorite ball, with four legs thrashing in the air. Give it a try, it's cheap and you've got nothing to lose, except maybe a little dignity if anyone sees you in the act. Good luck!