If the only fabric between your vagina and his penis is his underwear, that is not a lot of protection. If you can feel his underwear as being wet, that means his secretions have come through his clothing, and should not be touching your vagina. It would be a difficult way to get pregnant, but if his penis is emitting pre-ejaculatory fluid, it is not impossible if the fluid reaches your vaginal secretions. Please get some sex education (there are good books written for teenagers) so you understand your cycle, when you are ovulating, and the risks of genital contact, even through (some) clothes.