Pain in right knee. Me what should i do?

Sir, I have moderate pain in my right knee only, but while bending there is cracking sound in both knees. During cold weather right knee's pain slightly increases and also it feels some inflammatory inside. I consulted a orthopedic doctor and he advised me to have x ray. And then advised me drugs (OSTOMA PLUS, ECOTOX, RABIKEM DSR, AND DICEF TAB) each 30 tablets for 30 days. But after taking all these medicines I don't feel any improvement. I asked another doctor who advised me to have CALCIUM 500mg + VITAMIN D3 500 iu tablets for couple of months and do some light exercise. Plz suggest me what should I do? My age is 26 years, weight 60 kgs, No one in my family has this problem, No injury or accident happened. BUT AS I LIVE ALONE AND GENERALLY HAVE FOOD IN HOTEL, SO THERE IS IRREGULARITIES IN MEAL AND ALSO DON'T GET PROPER DIET. (for last 10 years)