Because every knee is different, and every person reacts to pain differently, there's no hard and fast date to say when your pain will subside. It will fade and eventually be gone, but no one can tell you whether that's two days, two weeks or two months after the surgery. But, the likely reason it hurts more now than in the first day or two after surgery is your doctor probably put in a block during surgery and that block wore off, so now you feel the pain. My advice to you is to make sure to stay ahead of the pain by taking your prescribed meds on time, before the pain hits. If you're prescribed a pain med on a four hour rotation for instance, take the pill right at four hours, so the pain doesn't hit you like a brick, and then you have to work try to get it under control.
There will come a day when you can go longer and longer between doses; first as you find yourself forgetting to take them once in a while, to where you realize you haven't been in any significant pain and don't need pain relief around the clock any longer. It's similar to the question of when you don't need a particular walking aid; when you find yourself forgetting, for instance, a cane, and when you think about it have to go hunt it down where you last left it, that's a good clue that your dependence on it is lessening, and are on the way to not needing it at all.
I also suggest you spend a lot of time icing and elevating as that really does help with pain. I took no pain meds at all this last time around as I am unable to take any at all, so ice and elevation was the best, and only, way to help with any pain I had. Read the articles Jockette left you, especially the activity progression one. I read that one every single day during the first weeks and months of my recovery so as to remind me not to do too much, or too little, at any given point in my recovery.
I promise you, this will get better; but it is a roller coaster recovery and you will have days when you feel on top of the world, and days when you want to crawl into a hole and pull it in after you. But taking your life back is the end goal, and in order to reach that goal we have to go through a time of frustration, pain, lack of the ability to do the things we want to do, tears, pain, and oh, did I mention this recovery hurts a lot at first? This forum is here to help you with any questions and listen when you need to vent, as every one of us has gone through the surgery and understands what those who have never gone through a TKR recovery can't understand. Good luck and keep us posted on how you do!