Psychological Egoism Vs. Hedonism

Long time before I dared to enter my first philosophy class, I frequently was involved in friendly, but at the same time passionate discussions with friends and colleagues, holding fast to my strong belief that altruism merely does not exist. All actions we think to be altruistic, I argued, come from some self-interest. Now, of course, I identify this belief as psychological egoism.
Maybe, it could be argued, that my persistent denying of altruism and defending egoism was the outcome of my naivety, my infant ignorance of the deeper layers of the subject which can only be cognized through a scrupulous study of philosophy. Of course, someone may consider my arguments superficial and complete oversimplification of a composite topic. Probably the same can be said regarding my current point of view. After all, I was only paddling in the study of philosophy.
After a survey of the works of philosophers such as Jeremy Bentham, Joel Feinberg, Elliott Sober and Joseph Butler, who wrote just about psychological egoism, and having read some more indirect writings about this matter from J.D. Ross’s, John Stuart Mill’s, and Immanuel Kant’s books, I became even more convinced that every person's primitive motivation in any action is self-interest. Moreover, I am sure that the only self-interest that all we have is a delight, or avoidance of pain. And realization of all this facts makes me, therefore, a hedonist. So, I made up my mind to write a book where I was going to investigate the matter thoroughly and differentiate between these two notions relying on irrefutable facts got from personal experience, statistics and the observations of the outstanding specialists in this sphere.