Feeling happy about one's good actions

Sometimes when we have done a good deed, or have said a good thing that is only for Allah's pleasure, we often feel good about what we have done, and sometimes these thoughts stay in our head for long. Please I want to know, is this associated with riya? Can my good deeds become invalid for this reason and how should I stop this "Self-thinking-Admiration" process. And also please can you help me with a link to download a book on riya in-depth. May Allah Reward you.