Suggest Treatment For Persistent Swelling In Right Knee

I have had my right knee swollen 4 days now. I did not have any apparent injury, or hit anything. I have had to put more weight on it in the last 2 months cause I had a ting able fall on the other foot causing a midfoot sprain. This swollen knee situation started Thursday evening, pretty much out of the blue. During that day I had to kneel down for long and maybe sat in a wrong way(?) Though I did not have any pain till later in the evening. I ve done the RICE thing as much as i can and been taking ibuprofen every 6-8 hours since then. Hasn t gotten better, and its been hot and red -when i press over the reddened area that bit goes away but let off the pressure and the red pops up again. I m worried cause I read there may be an infection from the much I understood. I may be able to go to a free clinic on Friday. It hurts at moments. Especially after having let my leg rest horizontally on the bed and stand up again, it lasts a while and then goeas away. But the later in the day it goes, it gets more uncomfortable, especially if I don t wrap it tight with a bandage. The swollenness has extended to the ankle. And it feels a bit tender/sensitive.