Laura,
How are you doing your weight training now? Are you working one body part a week? Are you doing splits or are you doing total body workouts?
I think what you need to do is up your weights, take longer rests and work your upper body twice a week. Do something like this using the GS series:
Mon.: Chest & Tri's
Tues: Cardio
Wed: Back, Biceps, Shoulders
Thur: Cardio
Fri: Legs
Sat: Rest
Sun: Cardio
Add ab work in there at least once or twice a week.
Again, work as HEAVY as you can with each exercise. Take a longer rest then Cathe does. GS will give you excellent results.
Follow this for 4 weeks. Keep track of the weights you use and up it at least 2% each week. So if you use 20# dumbbells for one exercise for chest work, try to use 22# the next time and so on. You'll be amazed as to how heavy you can lift when you put your mind to it. I use 1# magnets to up my weights by 2#.
If you have any questions, please ask.