Tracie, I would go to a doctor at once who is knowledgeable about sewer gases. Start with your home, personal physician. I would only contact a plumber in this type of case if you need something fixed. You say you are having that done so that is good.
I'm not a plumber nor do i aspire to be one. I am a chemical Engineer and know enough to surely say that methane is bad for you. JJs post isn't off the mark. Sorry jc but other than recommending she have the tank inspected I dont see any place where he is recommending her to fix her plumbing. I think the symptoms jj is referring to is the fact that vents are missing. Yes, she already knows that and is taking steps to fix that. I think JJ is only agreeing with her when he says she ought to fix the symptoms, or the missing vent(s). I'm not trying to come between you guy but I thought as a third party that's passing by, I'd offer my Tuppence.
Besides, I though all you guys got along. Did I miss something especially between you and jj? Have a nice day I hope you do. david ;