31 pounds in 34 days? Yes, you did it before... but now look where you are... back to the beginning. If you dont do something you can sustain, you will keep gaining all of your weight back... possibly plus some. That is unhealthy and will do nothing but break your spirits in the long run.
As for the Phentermine, I have taken it and it doesnt work as well the second time around for some reason so I stopped taking it all together. I have heard this with many people.
I hope you find something that works for you