A couple of things come to mind. First, how about standardizing on one brand and type of film, and that manufacturer's recommended developer, rather than trying to chase things around. If you are going to be doing outdoor work, how about a 100 to 125 ASA film. For lower light, stay with the 400.(posted 8881 days ago)Next, how about your meter? Is it an in-the-camera meter, or a separate hand held one? Are the batteries fresh, and is the meter calibrated? (Fairly easy to do over the counter at a good repair facility or camera shop who knows their stuff)
While you are there, have your shutter tested too.
Take a look at one of the rolls that is all dense and ugly. Does it look like it has a foggy, hazy black area all around the sharp edge of the frame? Or is the frame edge still sharp? If it is foggy, it probably means overexposure -- light meter or shutter need attention. If it is sharp it probably means over development -- too strong a dilution of the developer, too high a temperature or too vigorous agitation or a combination.
Probably best to start over with only one brand and type of film and developer and keep everything constant. Use the manufacturer's recommendations for everything first. Then change one thing at a time and keep good records of what you do. Shoot a "slate" or clipboard with all the information about film, exposure etc. If you start tossing things out at random, you may solve the problem but you won't really know which it really was.