Desperately need advice. Strange odor in m. bathroom.

Hello, thank you for taking time to read this post. I ran out of options and need to ask to advice. I am having a problem with a strangest thing that happens in my m.bathroom. When it gets warmer and we open windows we are getting a strong odor in the m. bedroom that has a sulfuric component to it but, I do not think it is a sewer gas. It is a little bit like natural gas but local gas company checked it out and they do not detect it.

It is even more noticeble when it is warm and windy and windows are open and there is a fresh air exchange.

We moved into this house 8 months ago and had this odor in early fall but then it got colder, we closed windows and through the entire winter we did not smell it ever. Now spring is here in Illinois and I just do not know what to check.

One suggestion was that it was a paint that when it reacts with oxygen, emits this odor...

House is 11 years old. Drywalled bathroom with painted wall.

Any help on what to check is appreciated. I have been lurking on this site for a long time but never asked.

Thank you in advance for your thoughts...