If your level has dropped 3" over a few weeks I would not sweat that. We are not that far apart and I would consider that normal for this area.
My wife thinks our pond leaks because the seasonal creek behind the dam keeps water in it now where she recalls it used to go dry during very dry times. She quite probably may be right, but our level drops in this pond is comparable to our old pond an eighth mile away and comparable to other ponds and pits in the area, so I don't worry about it. We did run into gravel at the bottom of the pond that likely connects to this small stream bed gravel and it was very difficult getting clay packed back in over it because of wetness, so I suspect we do have some connection with this small stream. But like I said, our pond does not seem to drop any more than anyone else in the area.
If we get wind, we can get considerable water loss from evaporation.
