Hi,
Thanks for writing in.
From your description I assume that upper abdominal obesity is your problem.
This is typically described as male pattern of truncal obesity. Now the if you have been having it for quite a few years then it will be very difficult for you to shed the fat.Excessive exercise will not help in any way as it will cause more strain on your knees which should be avoided at all costs.
I would suggest the following.
1. A diet scientifically devised by a professional medical dietician taking into consideration all morbidities.
2. A short duration workout just to keep fit again devised by a physiotherapist taking into consideration your weight and level of physical activity.
3. For the constipation problem , plenty of water, high fiber and a mild laxative like lactulose would be ideal.

I hope this answers your querry.
With regards

---