I hope someone can help us finally solve our odor issue!

About a year ago, we noticed a bad odor coming from the toilet. It smells like methane. Sometimes it is not so bad (can barely smell it) and other times it is HORRIBLE. It usually smells the worst in the morning, especially after we take a shower (the bathroom is more humid then, of course).

The only thing I can think of that changed is we re-tiled the bathroom a little over a year ago, and of course had to take off the toilet. My boyfriend put on a new wax ring when he put the toilet back on.

The smell seems to be coming from the base of the toilet, so I have caulked that thing as much as I can so there are no openings. But we are still experiencing the bad odor!

I've read other articles where they say the problem is likely the was ring. Can anyone tell me how we can tell if this is our problem? And if it is, how do we put a new wax ring and make sure it doesn't happen again?

Any help is much appreciated!!