I'm on my 6th day now of Adderall XR, but I'm finding that the effect seems to be decreasing each day. The first day, I could really feel the meds 'kick in' and wear off, but today, I'd be hard pressed to put a time on it. I didn't feel much better today than I do without it. The only thing is that I'm now feeling completely wiped out, so I don't know if maybe the adderall is only just keeping me above water to compensate.

Is this a normal effect? Do I need a stronger dose? I'm on 25mg at the moment.

The only thing I can think of that may be causing problems is that my appetite has been seriously affected, and as such have not been eating much at all.

25mg is a fairly high dose, depending on your weight, so it's not that the dose is so small you don't notice the effects. The decrease in appetite is almost certainly due to the Adderall. You may feel wiped out when the drug starts to wear off - this down feeling is a common complaint - the extended release is supposed to minimize this effect - you just get it at the end of the day.
Give your body some time to get used to the Adderall and see if you are getting any benefit. Stimulants help 60%+ of the people who try them, so it is possible that this particular stimulant may not help you - but something else might.
I'd give it some time and talk to your Dr.
Good luck
Greg

Thanks Greg. I'm definitely willing to give it a go, but the appetite thing's really beginning to worry me. I'm just not eating at all, and since I started last Wednesday, I've lost 8 pounds. Don't get me wrong, I won't miss them ;) but I don't think to lose that much in a week is terribly healthy. I'm 134lbs at the moment - is 25mg still too much?

At 134 lbs, 25mg of Adderall is a pretty close to the max recommended dose (around .5mg.kg/day) - not that people don't exceed that dose. Had you tried a smaller amount?
8lbs is a lot to lose in a week, especially if you are 134lbs to start. I can easily lose a pound a day if I stop eating, but I'm 270lbs! Try eating a big breakfast before you take the Adderall, and force yourself to snack, if you can. You might want to try high calorie type foods - stuff like "Ensure" , or other meal replacement bars or shakes during the day, and try to eat as large a dinner as you can - once the drug wears off.
Good luck,
Greg