I don't think stress is a trigger, but I would be very surprised if it didn't have an effect on the frequency, duration and severity of mood swings. Something to note about the article I am about to link to - it looks very much like it was put together to hawk all the questionable supplements it has ads for all over the page and uses a big font to give them more real estate, but it is surprisingly well researched. The numbered citations generally lead to scholarly papers to back up the claims about what stress does to your blood, brain, hormones and whatnot. What they don't have is links to prove that what they are pushing does anything to help.
https://bebrainfit.com/effects-chronic-stress-brain/