healing crisis?

Hi everyone, I am 59 years old. I became vegetarian at the age of 19, vegan at the age of 25. Several years ago I was living in a very hot and humid climate, eating lots of fruit and feeling great. I worked hard taking care of several hectares of gardens and orchards. I was living on a raw diet, mostly fruit. I found that I got tired very quickly and had to eat lots of bananas to keep my strength. Because I was sweating a lot while working in such a hot climate my weight dropped to 67 kg. I am 182 cm tall. To try to regain some weight and body mass I began eating yoghurt. My weight rose to 75 kg. Some time ago I moved to a cold climate area and in November 2015 I once again became vegan as I no longer had to worry about being too thin.

About two months ago my knees became very painful and now whenever I walk I am experiencing a lot of pain. I worked my knees very hard during my younger years carrying water for irrigation up a steep hill from a river. I am wondering if anyone else who has transitioned from milk products to vegan has experienced a problem like this. Could it be something like a break up of uric acid causing the pain?

Any replies are very much appreciated.