Maybe it's a reaction to the adhesive on the dressing? It sounds like a blister. I've had problems in the past blistering at the edge of a dressing. I wouldn't pierce it as that will put it more at risk of infection. Might be worth getting checked as soon as you can to be on the safe side. They may need to use a different dressing,
Wow, that all sounds great. Don't overdo things now. It's easy to get carried away when you're bored. Can you find something to do to occupy your mind?
@zab, work after barely two weeks? Are you crazy? I went back to work after 4 weeks. First week back (week 5 post op) was from my home office, the next week (#6 post op) alternated office and home, week #7 was full time in the office. I have an hour+ drive to and from the office. I found that transition tolerable mainly because I have primarily a desk job and was able to elevate and ice whenever needed. Not knowing what you do for a living, I would strongly recommend you reconsider going back to work so soon, at least not full time.
You are at that point in time where you think you are well on your way through recovery, which also means you are at a higher risk of over doing it. Depending on how much you over do it, you are bound to experience some setbacks which you will need to expect.
Don’t be in too much of a rush just yet. Your knee is still tender and easily aggravated.
It's always nice to have a good check up with the surgeon as there are so many bewildering experiences with TKR. You're through the acute healing period. The next 3-4 weeks there is improvement every day. The tissue are still raw and will rebel with any amount of overdoing. The ice and elevation is still important, and 30 minutes is only enough time for the cool to penetrate, not enough for it to have much effect on the inflammation. My minimum icing time is 60 minutes. As good as you feel, it's still 50 weeks until you're knee is fully recovered.

@Josephine, is this true?now I'm past that acute pain phase 30 minutes is plenty long enough icing reduces blood low around the wound something I want to avoid as much as possible to aid the healing process. Reduced blood flow = reduced healing time if you see my reasoning and everything I've read and been told backs that up.