Yes, you can most definitely use it more often than every 2 weeks! 
Assuming you keep your starter in the fridge between baking days:
- take the starter out of the fridge and let it sit out at room temperature for about 2 hours to warm up
- then, feed your starter with equal parts of flour and water, stir well, beating with a fork or spoon to get some air into the starter
- let the starter "work" and expand for 2-4 hours, at the end of this time it should be very active (bubbles on surface) and expanded somewhat in the container
- now you can measure out the starter needed for your recipe (usually this is about a cup) and make & bake your recipe
- after taking out what you need for your recipe, you can cover the container (glass or pottery - NO METAL) of starter and store in the fridge until the next time you want to bake a sourdough recipe
- if you only have a few tablespoons of starter left in the container, you can feed it again, let it work another 2-4 hours, then store in the fridge.
Hope this helps!
Teresa (peepless)