I started getting them when I had my first child. At first they were just once every 3-6 months, then once a month, then....and I hate to tell you this....about 17 days a month. (The time spread was about 12 years.) And yes, my period was the biggest trigger.
I got imitrex, and it worked really well for me, as long as I took it quickly enough. It still works, actually. The problem is, it wouldn't prevent another one from happening the next day. There was a two year period recently when I felt like I was going to go crazy with migraines almost daily. I'm not sure how I managed, but I did.
I tried everything -- 4 different preventative meds, physical therapy, chiropractic, and accupuncture. Nothing worked except the physical therapy. I loved getting the PT massages, which were amazing and made a big difference, but insurance only paid for one month of that.
So my neurologist started giving me botox shots every 3 months, and one year later, it really started working. Now I have migraines 1-4 times a month. Yes, it's a pain if I have one each week, but it's so much better than 17+ days a month that I don't mind.
Other triggers for me (besides my period) are stress and lack of sleep, so I try to be good about staying calm and getting rest. Good luck!