This may be something of a long shot, but...

Could your mystery odor be coming from the heating system? I once tracked down a plasticky odor, a bit like new carpeting, to frying insulation on a furnace blower motor.

If you can't stand to smell it then you're going to be at a disadvantage in locating the source and might want to bring in someone else to help with the sniffing. I'd proceed by keeping track of when and where I smelled it. If it was uniformly strong all over the house, I'd assume that either the heating system or some kind of draft was helping to circulate it. If it dissipated when the heating system wasn't in use, then appeared first near the heat vents, that would pretty much finger the heating system as the suspect. If it was strongest in one room, that would obviously be the place to focus.

If it did turn out to be neighbor-related, that wouldn't necessarily mean a drug lab. Some crafts use lacquers with acetone-like solvents, too. In that case, I'd hope they were taking precautions not to brain-damage themselves or burn the house down.

Good luck, Shangrala, and I'd love to know what you figure out.