What Could Knee Pain With Rashes Indicate?

For about a week now I have had painful knees and the tops of my legs whenever my knees have been bent, such as sitting or squatting, even sleeping with my legs up. I also have a slight rash on the tops of my legs, looks like little goosebumps but a bit red and like sores. I am 29, around 164cm tall and weigh approx 42kg. No previous leg problems.