Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine you and obtain a history, I can not tell you what the exact cause of your symptoms is. However I will try to provide you with some useful information.
As you mention, the possibilities for your symptoms do include migraines, TIAs, and another possibility though less likely is seizures. Opthalmologic problems (related to the eye itself) rather than neurologic problems are a possibility as well, though less likely.
Ocular migraine (also known as opthalmic migraine or ocular migraine) is thought to be a variant of migraine in which headache may or may not occur, but there is often a family history of migraine disorder. It is a difficult diagnosis to make as there is no specific test for it, but if other causes of vision loss are excluded, the diagnosis may be invoked. It is more common in women, and symptoms may include transient vision loss, flashes of light in the peripheral visual field, or other similar symptoms lasting usually 30 minutes or less. Headache may or may not begin within 60 minutes and is often one-sided, throbbing, and may be associated with nausea and light-sensitivity. Different migraine/migraine-variant triggers. If these migraines are severe, sometimes migraine prophylaxis with medications such as calcium channel blockers such as verapamil may be helpful.
Distinguishing between migrainous phenomena and TIA is sometimes difficult, but the exact progression of symptoms, combined with other features, helps make the diagnosis. A history of migraine headaches in the patient or many family members, combined with stereotyped events (similar symptoms occuring over and over for years since a young age) favor migraine. A TIA, or transient ischemic attack, is due to a transient decrease in blood flow to a part of the brain. The symptoms that occur depend on which area of the brain is not receiving blood. TIAs are typically not associated with headache, so in the presence of headache, complicated migraine becomes more likely. TIAs that present strictly with visual symptoms such as flickering lights or colorful patterns are also unlikely.
Overall, given your symptom description and the length of time you have been getting your symptoms, a migrainous phenomenon (aura without headache) is high on the list, but TIAs do need to be excluded/investigated. Investigation of your symptoms to exclude other possibilities is recommended, and evaluation by a general practioner with referral to a neurologist and eye doctor as indicated would benefit you. Often, testing of the blood vessels to the brain, and other tests to exclude identifiable causes of TIA is necessary, particularly in someone who has risk factors for stroke (older age, smoking or prior smoking, diabetes, hypertension, high cholesterol etc). Treatment with a medication to help prevent stroke (such as antiplatelet medications which"thin" the blood) may be indicated depending on your history/other medical problems.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.