It's for my my first time dating and i don't know what to talk to my gf about?

Hi, I'm 17years and it's for my first time dating.my girlfriend thinks i'm ashamed of her cos i never call her at school on break times.it's the truth that i never call her but i'm not ashamed of her,the reason i do that is bcos i don't know what will i say to her.i always see my friends call their gfs on break times and i wish i could know what do they talk about so that i can also talk to my gf.i don't even call her bcos i still don't know what will i say to her over the phone .PLEASE guys i need you to tell me atleast five things you talk with your partner about when you are on a serious talk.NB: NOT PICKUP LINES