You say that you've been following phase 3... so keep in mind that phase 1 losses are mostly just water weight that we lose when we drastically change our eating habits. If you have been moderately following a south beach life style you will not see the same results that you did the first time around..... that doesnt mean SBD isnt going to work for you, but that your body doesnt have that same need to "detox" as it did the first time around.
I do think that the older we get and the less that we have to lose does make the process more difficult, but certainly not impossible.
I agree with Jekel, if you are willing to post a few daily sample menus, it may help us to see if there is any advice we can give to help you narrow down what the culprit (if there is one) may be (again, keep in mind what worked for you last time may need refining now if you have been eating somewhat healty)
173 as of Mar. 24... April goal, down 5lbs