As a part of my thesis research, I need to mention what are the reasons that make it uneasy for humans to talk/think about sex. Why is the topic usually provoking stronger reactions (both positive and negative as well as personal and outer) than e.g. weather. 

I have found academic materials that state that sex reminds us of our corporeal animal nature and it provokes the fear of death, while we prefer to manage that terror by clinging to a symbolic cultural view of reality. But I don't think this is all. I can imagine there is some term that investigates the problematics of sex as a topic in human's mind. I tried to find something on google scholar, but I wasn't succesfull. Any ideas? Recommendations? 

  That would imply that it is at least as hard to talk directly about death as it is to talk about sex.  That is not my experience!  I think you need to consider the enormous emotional impact of sex.