It sounds like something is causing your film to be overexposed.

Just because the camera wasn't doing it before doesn't mean something hasn't gone wrong with the camera, particularly since it seems to always be doing it now. That also goes for your processing lab.

Some things to check:

• Is the aperture stopping down to the selected setting just before the shutter opens? The linkage in a Konica Hexanon 40mm f/1.4 broke on me one time and I almost went crazy testing the camera's meter trying to find what was wrong before I discovered the problem with the lens.
• Is the shutter operating correctly? Or is the second curtain possibly dragging too slow? If you can find a shop that still does it, consider having the shutter timing tested.
• Is the film speed selector working properly? Does the same scene meter differently if you change the film speed setting?
• When's the last time you tested/changed your light meter's battery? If you leave the lens cap off a lens attached to your camera, or allow light to shine through the viewfinder, it will drain the battery fairly quickly (over several days or weeks).
• Another common problem is that the connection between the battery holder and the wire that leads to the meter circuit gets corroded. Cleaning and resoldering it will sometimes solve an issue with the light meter.
• If you have a shop in your area that does it, have the light meter tested.

If you've not had a roll from one of your other cameras properly developed since the two rolls from your K1000 came back overexposed/overdeveloped, also check with the lab to be sure they haven't changed anything. Someone may have accidentally mixed a batch of developer too strong or used one kind that needs a shorter development time when they thought they used another that requires longer development times.