Reason for the odor. It is noticed in the morning 8 ish to 11 ish oclock. Then it disappears. Doesn't happen every morning.. Sometimes it is when it is sunny.. sometimes when humid.. sometimes when foggy... or rainy... There is not a finite pattern to when the smell will appear.
It is contained in that one room. Upstairs just above this bedroom there might be a very faint smell of the same. Please help me to resolve this mystery, it is driving me crazy!

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There is not a finite pattern to when the smell will appear

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And that's what makes it hard for us to help. We're not there to localize the odor. You have to do that.
Once we know the source, floor drain, shower drain, toilet,etc. we can began a repair. Sniff around for the strongest smell. Look in 5the attic for a open vent. Anything we can sink our teeth into. Good luck, Tom

I can only think of 3 things it might be, it will give you something to look for:

(1) If you have carpet, have a look under it to see if any damp has appeared.

(2) If you have any plants check to see that the soil has not produced mildew.

(3)
Have a look at light fixture on ceiling, if it's a plastic fixture, these can give off a fishy smell after years of use (I know this one sounds funny, but I encountered it in a friends house).

This odor is contained in a bedroom only that faces the street. To describe the odor the best I can would be it smells of sewer or rotten egg gas and is sickening. The upstairs is unfinished with only electricity. My home is well maintained without leaks or underneath moisture. I sincerely hope this further explanation can help.

Would the house clean out be located under that bedroom wall?
Is there a bathroom overhead? Back to you, Tom