There are a few that you can find on Google Scholar that explicitly mention the mouth as a sexual organ, but they are largely based upon the works of Freud or some earlier, more…”interesting”, points of view.
I don’t know what resources you have available to you, but if you’re on a high school or college campus, you probably have access to a lot of different journals - I just don’t know which ones you can access.
Beyond Freudian stuff, there are two broad approaches to seeing the mouth as a sexual organ; it can either be viewed as a site of physical stimulation or chemical stimulation (the body responding to a partner’s MHC profile/hormonal profile and *possibly* [not very likely] responding to the pheromone signals via the human vomeronasal organ).
If you’re looking at it as a site of physical stimulation, try looking up the works of Kinsey, and the follow-up research done in the 1990s that heavily references Kinsey. Chemical stimulation articles can be found in the Chemical Senses journal, among others, by searching for “MHC human sexuality”, “human vomeronasal organ”, and similar terms.
The mouth is also seen as a sexual organ owing to its aural stimulation abilities when producing sounds during intercourse or even in non-sexual interactions. However, this is not a widely-researched view.
We once had a chimp who could sort photographs of apes and human beings into two piles. Apes on one pile, humans on the other. The only trouble was, every time she got to her own picture, she put it on the pile with the human beings.