If your CYA was low, your chlorine could have dropped to the point you are now fighting some contamination in the water that is consuming all the chlorine your cell produces. The only way to know whether it's a bad cell or something else is to get a full set of test results.
One way to tell if you are fighting an algae problem is to take a chlorine measurement right after dark in the evening. Then take another one early the next morning before sunrise. If two differ by more than 1 ppm FC then you have an infestation and need to shock.
If you have a Jandy system are you getting a "service" light? After you get your water balanced and still have problems, look at the back circuit board. Ours had two blackened diodes. New part has been shipped. We are certain this was our problem all along.
A quick way to tell if your cell is producing/depending on the cell type, is to crack open the union that leads away from the cell while it is running and collect some of the water to test for Chlorine, It should be a lot higher than the pool water if the cell is working well. It's pretty simple and foolproof.