You'll have to take a water sample to a pool store to have the water tested for CYA. We really need that number to recommend a shock level of chlorine.

You need a good test kit ASAP. Ben's kit from poolsolutions.com is the best. The Taylor K-2006 is also very good and the Leslie's FAS-DPD is also (I think it's a re-branded K-2006). In the interim, you can use a local pool store for testing or get the Wal-Mart 5-way test kit (OTO chlorine testing so of limited value for chlorine above 5 ppm).

Read the sticky threads at the top of the chlorine and testing forums; great basic information in those.