Hello
As you  mentioned that once in a week you got "giddiness" and 
vomiting and a sound in your right ear.
You took treatment as well as  M R I with no finding .
Giddiness is related with a reeling sensation & feeling as being to fall . 
When such type of symptoms present may be due to these reasons , these includes.
1 Hyper tension , diagnosis can be confirmed by examination at the time of incident as well for 3-4 days regularly .
2 
Hypoglycemia is another most common cause . Get in blood sugar level.
3 Hyper acidity or 
gastritis is the another such cause.Whenever you feel such symptoms take some 
antacid .
There are so many reasons as , tension, Minere's disease , vestibulococchlear nerve impairment .
Since your age is very young so in my opinion consult an E N T and get his opinion.
When such patient visit in my clinic I usually prescribe 
betahistine 48 mg twice in day for 10 - 15 days with pnataloc- D once in day.
Hope this information will help you.