I'm very surprised the doctor told you that. If you use Orlistat correctly you can actually loose quite bit of weight. I was on it for about 8 months once and lost over 3 stone.
The thing with Orlistat is that you have to be really careful about how much fat you eat per meal. If I remember rightly you shouldn't eat more than 5g of fat per meal otherwise, yes, it does give make you go to the loo. And believe me, it isn't pleasant! It does restrict you quite a lot on what you can eat but if you are willing to stick with it, it does work.
I am really, really surprised that the doctor just told you it would make you go to the loo and didn't go through how to use it properly. I got loads of help when I went on it and even got regular phone calls from the company that make Orlistat to find out how I was doing. It might be worth going back to your doctor and questioning it.