The one thing that's guaranteed with migraine is change. It appears that nearly any change in our environment can trigger a migraine attack. If this is a new routine for you, then just the change alone can set off an attack. I know you asked some specific questions. They're really best answered by your headache specialist. Perhaps I can provide some insight to help you find the answers.
1. Always report any change in symptoms to your doctor. It's probably nothing to worry about, but he or she might have some pointers. I love it that my headache specialist is also a migraineur. He lives it and has his own "bag of tricks" that he shares with patients. Maybe yours is, too.
2. There are specific guidelines that determine whether or not you need a preventive. In general, more than 4 attacks per month warrant considering a preventive. Most people don't realize that it's better to treat this condition early and aggressively to prevent it from becoming chronic. Preventives are not something you consider based on triggers, but on the frequency and severity of attacks.
I know this site is big and it can be hard to find answers, so I've included a couple of links to help you in your search. Please let me know if you have follow-up questions.
https://migraine.com/blog/new-migraine-prevention-recommendations-from-the-american-academy-of-neurology/
https://migraine.com/blog/migraine-triggers-5-ways-to-deal-with-exercise-as-a-migraine-trigger/