Are you chlorinating with Tri-chlor pucks or Di-Chlor powder? If so, both are very acidic and lower your pH.

If you have acid rain in your area, that can be a contributing factor as well.

Checking your test kit is a good idea. I have several differnt kits so if I'm not sure about one, I can use another to double check.

Post ALL your numbers and maybe we can see something. Post whether your pool is vinyl or not, if you use a SWG, IG or AG and how many gallons.