We periodically have a fairly strong smell in our master bathroom after mild rain or when the temps cool down. Sometimes we notice it after we do much laundry or dishes. I can see the shower has a trap that has water in it and have never heard/notices any bubbles of gas coming from the shower or any of the drains. I can hear the gurgling sound on the toilet vent pipe if outside when flushed. We've not had any issues with sewage backing up into any of the sinks/tub/shower to this point. We bought the house about 1.5 years ago and have had this problem off and on, but never very consistent. Not sure when the septic tank was pumped last. Any suggestions would be greatly appreciated.

Sewer gas raises and falls with heat and cold. I would be looking very hard at the vents in the attuic. If one were left open or a break in a pipe that would give you exactly what you have. Durning warm or hot weather the gas stays in the attic and when it cools down the gas will descend to a lower level.
I doubt that it's your septic tank. Regards, Tom