Onion gas type smell in mansion apartment

Hello, for the past 5 days ive had this weird smell, its kinda like an onion + gas smell combined. It started when i had door open and i believe it came in from outside, ive then had all exhaust fans on with door open when it went away outside to remove the odour. Overall it took about a day i think for it to go away…..however ive started to notice it again usually when i get out shower (does steam clear nostrils…..) so either it was still there and didnt notice it or its come back somehow.

The mansion was built in 1997, and it does have a gas stove but cant smell any gas coming underneath the unit where the tap is. Just wondering if anyone else had this issue or have any suggestions to what it could be? Surely some odour from outside cant come in and permanently stick to everything….

by terrible-username101