It is true that in very rare cases, some women simply cannot breastfeed. However, it is far more likely that you are simply not used to it, and that a few minor changes to what you are doing will make it a lot easier and more pleasurable.Correct positioning and a good latch on technique will make all the difference.
In fact, nearly every woman out there is physically capable of breastfeeding and unless your doctor has told you that you cannot for some reason, you should assume that you can. A good idea is to visit a breastfeeding coach, or the La Leche League. Your midwife or nurse should also be able to teach you how to breastfeed properly, so that you child gets enough during a feed and you keep producing enough milk.