Sewer smell in bathroom

I keep smelling something REALLY bad in my bathroom! It smells like something died! I have heard about sewer gas smell. There is a pipe on the roof that vents the sewer gas, I think. How do I go about checking it?I live in a manufactured home, so I don't have a basement. There are woods behind my home. Is it possible that an animal got under the house and died? How do I check that out? I want to find a link to a handyman, someone who could answer my questions. The smell is only in the area of the bathroom, not anywhere else. I clean all the time, so it is not that I am a bad housekeeper. I really do need some answers right away. Thanks in advance for any help.