Suggest Treatment For Pain In Knee Along With Soreness

My right knee has been hurting me for about a year, lately I have a feeling of stinging and soreness and sometimes my range of motion is limited side to side. I have had it xrayed and they said it didn t show any signs of arthritis. At one point about a month ago I could not even walk properly because it cause soooo much pain in my knee, but my doctor said there was some fluid and put me in melixcom ( may not be spelled right) anti-inflammitory once a day, still very sore and some days walking is still painful. Sometimes it will give out . I am 55 yrs old and a 5,4 and 159 lbs, am working on losing weight