Hi Dee Dee,
It sounds like you would really enjoy a circuit training routine. If your gym offers a Boot Camp style workout or a strength/cardio class, then you might want to give that a try. For any strength training routines, you only need to work the muscles 3 times a week. Some people break up their routines were they focus on arms one day and legs the next, but then you'll need to dedicate 5 to 6 days to weight training. In 30 minutes you can hit all your major muscle groups and combine cardio. I just did an article on this for a home workout, but you can apply the same principles to the different exercise machines at the gym. I'm sure RWF has a couple of articles about it too.
Home Circuit Workout for All Moms
When picking exercises, look for the opposites. Most gyms have machines that show the muscles. You want to work both sides. For instance, biceps/triceps (front side of arm/back side of arm), abdominals (core)/Back, quadriceps/hamstrings (front/back upper leg), etc. The machines will give you ideas if you want to do dumbbells or bands instead.
Once you get the hang of the weight training, you're going to love it.