On the top part of my head (halfdollar size) I get a horrible/painful pressure that makes my right eye twitch uncontrollably. Could it be a brain tumor?

Unlikely! The typical pain associated wih brain tumors is generalized, worse in the morning and with all maneuvers that increasing pressure in the brain such as bearing down, coughing or sneezing. However, most tumors do not follow this typical description. Your pain is non-specific and should be checked out to make sure it is not something serious..