Yes, I think kids just go through these phases--extra stressors or not. (Though the things you mentioned are sure likely to trigger them!)
I do find it's important to do a little extra monitoring/mentoring during these times, rather than just "wait and hope it takes care of itself" just because, well, a), If it is stress, it won't go away on it's own, and I want to be there to help them work through it (positively!), and b) I think the fighting can kind of become habitual, if you know what I mean. So even after the stressors are gone, they continue to bicker just out of habit.
My girls are 6.5 and 3.5 and recently I've been having them do "replays" because I suddenly felt like there was a lot of hitting/pushing/otherwise hurting going on--like that had become the "go to" response when frustrated. I explained (again) that this isn't the way I want us to handle things, and I know we get frustrated sometimes, but we can learn to respond without hurting, and one of the ways we can do that is practice.
So when someone did hurt, I would say (kindly, and without that "no-no" type tone), "Okay, let's replay that without the hurting." Sometimes it takes a few moments for one of them to cool off, and that's fine--I don't push it if they're still angry, I know they'll come around eventually.
Anyway, it has really worked well. In the past week we went from several times a day to maybe once a day, or not at all.
Oh, and when I introduced this, to make it "fun" and kind of take the edge off the "chastisement" feeling, I told them every time they remembered to respond without hurting, they should "do a little dance" and say, "I did it! I can do it!" I didn't want it to become like a praise/reward-reinforcement type thing, I just wanted them to be able to notice themselves being frustrated but not responding violently. To be able to feel what it feels like, and to be aware that they are very capable of it. I also had them "do a little dance" after they did a replay too, so it wasn't like a conditional, "If you do good, you can do a dance, but ONLY if you do good"-type thing. Anyway, the dancing has worn off, I think they've forgotten about it, but it helped them take to the idea enthusiastically to begin with.
--Kate, home/unschooling mom two three girls (6, 3, and Tiny)