Breastfeeding tips

So I'm 20 weeks , and I was always not for breast feeding but now thinking about it , I may breastfeed while I'm with her but she will be on formula when with other people, babysitter etc. but I do have questions... does it hurt the first time??? My nipples are really sensitive, I HAAATE them being touched unless I'm having sex. Do they become not sensitive when they fill up with milk??? I'm so scared to breastfeed !! But I definitely want to know answers to those two questions please!!!