My knee to ankle Pain?

I give you history, I joined gym about three months ago and continued for about 20 days. On 20th day I did extra session of elliptical machine of 10 minutes also one more machine ( i do not know the name) on which you have to keep pedaling and your body moves up and down. It is work out which give stress mainly to the knees. After 20 days I stopped going to the gym for some reason.

After some days i found that from my knee ankle paining if seated for long time in one place. If you walk some distance it stops. Sometime it pains even if you are not seated in one place for long time. I went to the Doctor who told me that cause is exertion, and he gave me some medicine and told me to walk slowly everyday as much as I used to walk earlier for about 15 days and then gradually increase the speed. I followed his instruction (of course i did not go for walk everyday) but again the same problem. I again went to doctor and again he advised to me the same thing. Important point here is if you check any part of leg by touching or putting some pressure it does not pain at all. Now, it is more than one month. I do not know what to do. Shall be glad to know if anyone of you knows this ailment or suggest cure?

Additional point: every day I am on computer for 7 hours in office and 3 hours at home (sometime more). So is it magnetic effect of working on computer which coincided with above?