What could be causes of itching anus, dizziness and head pressure? All three presented at the same time.
Many things. Itching anus is most commonly due to irritation of the tissue in that area (hemorrhoids, tear (rough wiping), infection, dryness, rash) and may be visible with a mirror. It may be unrelated to other symptoms, but people facing crises can have all three complaints if rectal tension develops or they have to sit too much. Headache and dizziness can result from many things. If not better, see MD.
Circumstances? In your other question you indicated there were circumstances to the onset of these symptoms. Headaches and dizziness occur together often, the itching is not normally associated with the other two.
Even pinworms! I don't know any disease which would cause all three symptoms. Perhaps you have more than one problem. Itching around the anus might be due to irritation from wiping with harsh toilet paper or inadequately. Pinworms can cause this symptom. (That's more likely if you have exposure to children.) The other symptoms may be caused by very many disorders. You'll need a doctor to solve that problem.