First I would call my doctor, then I would call my lawyer and sue for damages. The harmful (and explosive) gas in sewer gas is primarily methane. See the following link for what can happen (besides ill health): http://www.stargroup.com/images/newsclip.gif
I'm not a doctor (and be warned not all doctors know about methane poisoning, so find one that does) but I think methane poisoning can be similar to carbon monoxide poisoning in that it gets into the blood instead of oxygen. Who knows what happens with longer term contact like you have had?
Also, depending on what else you put down the drain you could have all sorts of toxic gasses coming back into your living spaces.