Dont sweat it. Mine went away and now it's back last week. I'm 17 weeks. I didn't really have any with my last pregnancy but this time, it's definitely there.
No. It can go away and come back later or just go away. I don't remember ever getting sore nipples during this pregnancy.
No, I'm 33 weeks and mine haven't been real sore since the beginning, the further you get it may come and go with your hormones.