Hi Roxie,
Do you have any of Cathe's DVD's? Any of her ab workouts are excellent. I highly recommend the ones from Kick, Punch & Crunch, Step, Jump & Pump, any of the ones from 4DS as they work the lower abs really well, Muscle Endurance, Body Max 2, etc. These stand out to me because I feel they are Cathe's best.
How is your diet? Are you eating clean? Do you eat 5-6 times a day or every 3 hours? Are you on a workout schedule right now?