Don't be discouraged. You could have been that strong 2 months ago before surgery. The pre-op diet through to full foods you lose a lot of muscle. Shake it off an focus on the future.
I just bought the Polar H7 Bluetooth heart monitor for the iPhone and I am very pleased with it. Works with RunKeeper and the polar app works the same way out Polar set up works at Orange Theory. I think it was like $60 on amazon.