Can someone PLEASE help me.

First of all I will start out saying that I live in an older mobile home. Recently I had to replace the wax ring in my bathroom toilet because I was smelling these terrible odors through out the house. I thought that this would fix the problem but it didn't. I then had the spetic tank pumped out thinking that this was the problem. But again, the problem still remains. I have been crawling around the house to see if I can find anthing leaking or broken but, I can't find anything wrong.

I noticed, that while being under the house that I can't smell the terrible odor. It seems as though these odors are trapped in between the floor and the underhouse insulation and are being sucked into the house via the heating vents, although I can smell it really strong even when the heat isn't on. I can even smell the while walking around the outside of the house. I just don't know what to do anymore.

Can anyone help me with this? I am desperate to find the problem and fix it.

Thank you!