Gati,
The bipolar disorder should be treated by a psychiatrist who is familiar with the disorder and the various forms of treatment for it.
The Migraine disease may be treated by a family doctor or neurologist if the Migraines aren't too frequent and respond to medications. If a family doctor or neurologist isn't able to bring them under control, a Migraine specialist should be consulted. Take a look at the article Migraine and Headache Specialists - What's So Special? If you need help finding a Migraine specialist, check our listing of Patient Recommended Migraine and Headache Specialists.
It's important that these doctors consult on treatments, preferably in a conference call that includes the patient so the patient can participate in the selection of treatments. With appropriate consultation, it may be possible to find medications that can be used to treat both bipolar disorder and Migraine disease. Possibly antidepressants, neuronal stabilizing agents (anticonvulsants) that are also used as mood stabilizers, etc. If you'd like a list of potential Migraine preventives, take a look at Migraine preventive medications - too many options to give up!
Hope this helps,
Teri