Greetings, sorry about your knee pain.
Body weight has nothing to do with knee. It a very old outdated thought. Look at weigh lifters they take on huge loads on the knee and are heavy individuals, they do not complaint of knee problem nor their weight is a problem.
Next Steps
You see a sports physiotherapists and get your knee corrected. alignment of patella creates knee problem. correct it for which a physio will help you. a doctors role to treat your knee problem is limited unless there was an accident which caused knee problem. it is not mandatory to use treadmills for weight management. there are exercise without any equipment.
Health Tips
in 4 weeks you should see changes, if unable to find a good physio let me know will assist you.