I can identify with your frustration and regrets, and with your "cabin fever" at being confined to your home by ice and crappy weather! My TKR was last February, and I couldn't go outside for several weeks afterwards, because of successive bouts of freezing rain.
The things that helped: I focused on walking less, but better. For example, I took walks around our kitchen island, practising heel-to-toe steps and concentrating on normalizing my gait (which was terrible as a result of the old, arthritic knee). I already had an exercise bike, but I also went online and bought a used stepper ($30), and I'm still using both of them to this day (because I enjoy them, not because they're necessary). I started a weekly personal "recovery blog", in which I wrote about setbacks and improvements. The notes about improvements were especially useful: it's easy to focus on the negatives and forget about the positives - we all do it, because this is such a difficult recovery. But as time went on it was nice to look back at what I'd written and realize how far I'd come, even though it never seemed like far enough!
As for tendon pain: for me at least, it was a regular occurrence during recovery. My tendons had shrunk because my old knee was permanently bent, and it took many months for them to stretch and adapt to their new role. I also pulled my hamstring quite badly on more than one occasion. Even now, almost a year post-op, I still get the occasional twinge in some tendons and muscles.
One thing that has helped me has been to focus on function, not numbers. I'm not a very flexible person generally, and am not really expecting to achieve the flexion numbers that some people are able to get. Right now, at nearly a year post-op, my ROM hovers around 120 to 0. If I'd focused on the numbers, I might be disappointed. But: I can hike 10 km over rough, hilly ground with no pain. I can walk long distances at a decent, steady pace. I can jog and run for short distances. I can run (yes, run) up and down stairs with no problem. I can do heavy yardwork at home. I can ski (carefully). I can snowshoe. This year, I climbed a ladder and installed Christmas lights around our home's gutters. I can run my dog in agility trials. And most importantly, everyday life is totally pain-free and I don't take any medications at all, not even Tylenol. This time last year, I couldn't do any of those things and was taking enough painkillers and anti-inflammatories to kill a small elephant.
The early weeks are tough. Someone asked me, a couple of months after my operation, if it had been worth it. I told them they would have to chloroform me, tie me up and carry me to hospital in a bag to make me go through it again. And I still sort of think that. But it does get better. And it will be worth it.
Best of luck! Hang in there.