Believe it or not, I wasn't yet a full-blown movie geek in 1998. I didn't even start saving my ticket stubs until the summer of '99. In all fairness, I hadn't been quite old enough to go to the movies by myself yet -- not much younger than any of my colleagues in the summers they covered, but young enough to spare you the math.
Every third weekend, my younger brother and I spent with our father, and a reliable way to spend time together was often to go to the movies or rent something and stay home. So by only (probably) going to the movies every third weekend, I only saw maybe six movies theatrically over the course of those eighteen weeks. I'll bold those that I remember going to see as I go along, and then touch upon the rest of the releases in between.
(By the way: the weekends in the summer of 1998 happen to line up with those of this summer. Let's see just how far we've come...)