Dan welcome to the forum.
There is not set rule for lengths of migraine pain. www.mychronicmigraine.com/know-your-headache/?cid=sem_mcm_bin_s_1_1830
this link has some very good information on the headaches that I hope will help you.
I take imitrex for my break through pain. It works well. If you are not happy with your doc. I suggest a neurologist at a major hospital near you. They can sometimes find the root cause of the pain. Sometimes not.
However, usually they can stop the pain.
Peace and comfort