What Causes Dizziness Along With Clogged Ears And Headaches?

I have been suffering with episodes of dizziness since we went on holiday to Majorca last summer. It is sometimes accompanied by headache, nausea and a feeling of fullness in my ears.
My GP feels it is related to my sinus problems and recommended I take an antihistamine at night. This has greatly eased my symptoms but I still don't know what is causing them.
I went to see an ENT consultant this week who ruled out vertigo but was not able to give me a clear diagnosis. He suggested it may be linked to a new antidepressant I started early last year and told me to change it which I am loath to do as it took a while to find one that worked.
If that doesn't work, he is going to prescribe a migraine medication as he feels the dizziness could be caused by migraine although I don't get the bad headaches.
He could not see how the antihistamines could help but the fact is, they have greatly eased my symptoms. When the dizziness is very bad, I have to take to the bed and it lasts for hours.
I don't have much confidence in the consultant. Do you have any advice?