Please help! Toilet/shower/venting issues

I have had an ongoing problem with a smell coming from my shower drain. I had done everything to fix the problem myself but had to call in a plumber when it wouldn't go away. Since the shower drain was not clogged, he did not offer much help. He reluctantly snaked the shower drain and nothing came up. I told him I suspected it was a venting issue since I read up on it in this forum, but all he did was go outside and look at the vent (he did not go up on the roof or attempt to snake it). He flushed the toilet and pointed out that a big bubble came out after he flushed it but there was no stoppage. He left me a big bill and nothing to show for it. Last night, I noticed an odd sound from the bathroom and actually saw the toilet emptying itself, with bubbles coming up every few seconds. I flushed the toilet and the bowl filled with water without going down and almost overflowed. This morning, it was nearly empty again. Now I know I have a problem there and I really don't want to call in a plumber but it looks like I have to. I just want to pinpoint exactly what the problem is so I don't get the run around and pay for nothing again. Thanks!

I just had the city sewer maintenance check the outside clean out and they said it was clear of any blockages from my house to the main sewer line. So, that narrows the problem down a bit. The water in the upstairs toilet is slowly siphoning out and the sewer smell continues. When I call the plumber, should I ask him to snake the toilet and the plumbing vent? Any advice would be appreciated!

You have a clogged drain and the plumber did not snake the right line! Call him back to correct the error in his ways!

While it does sound like you have a clogged drain, smelly showers are just as often the result of improper construction. If the waterproof liner was installed flat on the floor rather than a presloped bed, that in itself after awhile will start to smell like a swamp.

Thanks for your replies. I plunged the toilet and the water finally went down. It's flushing now but still bubbles. My townhome is about 13 years old and I haven't had any problems until this past year with the shower odor.