Please please do see your GP, as soon as possible. Adult onset migraine is very unusual. There are so many other things that could be causing these attacks. Your descruption of nausea and dizziness being the main, or most distressing, symptoms suggests the cause may in fact be something else entirely.
I have suffered from migraine since age 9; I'm now 47. I am one of 8 children & we all get migraines, some more often and/or severe than others. The cause is genetic but the trigger for each actual migraine attack will vary for each individual. For some, certain foods are surefire triggers, for other lack of sleep (working shifts is a no-no), for others it's certain chemicals esp food additives. For me, sinus congestion and stress are my two main triggers.
As for symptoms, one of the defining characteristics of true migraine headaches is that they are one-sided, usually behind one eye. Another key symptom is light sensitivity; several posters have mentioned the need to lie down in a dark room until the attack passes. For some, that's a matter of a few hours, for others it can be days.
Does this describe what you are experiencing,
@Sara_H?
If your episodes are migraine, there are things that can help but it takes time to figure out what works best for you. Meanwhile, please do get a proper diagnosis - get a neurologist referral if necessary.
Best wishes, hope this gets sorted for you.