I'm a retired pilot, not a doctor.
It looks as though their assumptions may well be correct. It's incredibly bad luck being young and having achieved your ambitions, only to find you may well suffer from Classical Migraine.
I've written a lot about this on PpruNe medical forum over the years, and most of it not too encouraging. Indeed, it used to be a license loser, but these days I understand there is the possibility of regaining your medical, but being limited to a multi-crew operation.
I'm not sure which countries accept this malaise while flying multi-crew.
It's encouraging to note you did not suffer a severe attack. The aphasia is something that is frightening, but very normal as a secondary symptom/phase of the attack. So often, that part of it will not continue into later life, but the vision problems may well be a normal part of the attack as long as they last.
Very often the symptoms lessen with age. Indeed, you may well grow out of them altogether.
The most important thing is to get well. Quit cheese and chocolate for an experimental period. This will need to be for months, not weeks. However, it is my unqualified opinion that while some things may be a very definite trigger to migraine, and they are the main two I hear about all the time, the prime cause is deep underlying worry. This is quite different from stress.
An example might be the stressful time you have with simply getting to work, but deep down and more importantly, you are wondering about the long term problems of a career that leaves you having to do this desperately difficult commuting. I emphasize this is only an example of one thing being two quite different things in the mind.
You are right about other pilots being affected. Over the years, while spending long hours with crews in hotel bars etc., I gradually realized several of them were describing migraine attacks. I had watched someone I cared about having them, and I knew very well what they were talking about. It's all about timing. I'm sure some go on for years without it coinciding with a flight.
Everyone I've questioned about the problem give the same impression. During exciting and fun times, they don't have an attack, but during long boring and worrying times, they are beset with the problem, just at a time they need it least.
Take best advantage of the enforced rest period, and tackle the problem head-on and with determination.
Good luck.