Are you keeping a food log, or counting calories? The first place I would look at is calories. Back in the 80's, low fat was all the rage and people lost weight, and then they started eating all these new, great, low fat products - which in turn boosted daily calories. Alli is meant to deter you from high fat foods, which are also high in calories - but it's easy to substitute with low fat options that carry many calories themselves.
We're fat chicks, not doctors. Please see your physician before taking advice found on the internet.