Gratification symtoms in 5 yr old kid.

Hi I M mother of 5 yr old boy kid .. I have been seening since the a ge of 10 months my kid if he see the nacked stomach likes to sleep on stomach and kisses the stomach and starts strocks like as sexposter. To till date he is so ... Not only main who ever wear a dress of expocsing stomach he feels like go and touch it, kiss it ask them to sleep on bed so that he likes to sleep on there stomach... I m very much worried..if I ask him y our askng so means..he says I like to sleep on stomach . One of the doc I sent the vedio she said gratification problem.. I don't know what's exactly means and how to treat it Plz say how come we treat.. So many times I explained my child not to do so..do ask so it's nt good and counciled but no use Plz suggest me