Is it possible that duromine has no effect?

Hi, I am wanting to know if it is possible that duromine can have zero effect on someone. 

I am 40 years old, 170cm tall, and my weight is 120kg. The doc tested me for thyroid, diabetes and other things, and I came back all clear. 

The doctor prescribed me duromine 15mg. 

I am now on week 3, I have not lost any weight, I do not feel any extra energy, I don't have insomnia, or dry mouth, and i still get hungry before meal times. 

I wake up at 5am, take the tablet with breakfast, get ready, go to work. I am very active at work, walking 10 - 12 km a day. The other day, I actually fell asleep at about 10am, just sitting in a chair typing up a report. I eat lunch at 1pm, home by 4:30pm. 30 mins on the bike,Dinner at 5:30pm, and I am usually struggling to keep my eyes open by about 6:30pm. 

Today i am on an RDO and after going out to the shops, and walking around the park (7km), I came home, had lunch, then fell asleep on the lounge and woke up at 5pm! I don't normally have naps like that. 

I am wanting advise before returning to the doctor and getting another script next week. 

Should I continue?

Is it possible that it just makes people sleepy?

Am I on the wrong dose?