Suggest Treatment For Knee Pain Due To Workout

Hi,
I went to the gym on Sunday and my workout consisted of lunges, step aerobics, jogging and squats. Since then my right knee has had a slight pain in it and yesterday everytime I got up from my desk at work it slightly gave way as I walked away from my desk. Last night before I went to bed I put Ibulieve Gel all over my knee which has completely got rid of the pain but my knee has swelled. Please can you advise what is happening to my knee?