Please keep in mind that what works for some may not necessarily work for others. Some people have fast metabolic
rates and don't have to work hard to stay in shape. It can be the total opposite for others.
"Julian," make an appointment with your physician for a general check-up. Check your blood pressure, cholesterol levels, glands, etc. Only your physician can determine any physical roadblocks you may have; if any. Get clearance from your physician to exercise at will. Once you receive that, you can get started.
To fix the "problem" you're having, you'll have to severely modify your eating habits and add weights to your exercise routine. If it fits into your budget, hire a personal fitness trainer. Since you already know a simple workout isn't working out for you, you'll have to workout more often with more intensity. The basic three (3) day workout won't help you. You will have to lift weights three (3) days and do cardiovascular conditioning three (3) other days; then rest for a day. That may help until your metabolism speeds up.
Trust me, there is always a way to get results. But you have to be willing to do what it takes to get there. You must also be patient [it takes time] and exhibit a certain level of discipline with your eating habits in order to see results. Don't make the mistake of blaming your body. Your body normally just reacts to what you feed it and how you treat it with either an active or sedentary lifestyle. Think about that.
From my lips to your soul...
Redd