I Have A Painful Red And Swollen Area Inside Of

I have a painful red and swollen area inside of my right thigh that seems to get worse and I have no idea why it is there. The redness starts just above the knee and goes about halfway up my thigh and is 4-5" wide. I also feel like the area that is red is hot. I noticed this a couple days ago so I dont think it would much to worry about but wanted to check