Hey hun,
What kind of exercise are you doing? If you're noticing a difference in your clothes then maybe you are toning up rather than losing weight, as your muscle mass increases you may find that the fat you are losing isn't being shown as lbs lost because the muscle is replacing it - hence the STS.
I think the measuring is definitely a good idea and I hope it reflects the hard work you're doing.
You don't need to follow a strict plan for Xenical to work, and from what you've said it does sound like you are choosing healthy options. I'm counting calories to ensure I'm not eating too much, but if you stick to three meals a day that are low fat and don't snack, it is my opinion that you can't really go wrong.
I understand the point that Starlight makes that doing a diet plan in conjunction with taking the tablets will help you to lose but as long as you're eating low fat and not eating high sugar hence high cal content to make up for the low fat, you'd lose body fat for sure.
Don't give up hun, keep going and I reckon you'll see inchloss in two weeks time
xx