A nipple sheild is 'supposed' to be used when a baby is unable to latch without it, not for latch pain. That said, if using the sheild allows you to nurse and you otherwise would not be, far, far better to keep using the sheild than to stop nursing at the breast. Just make sure you are clear on the possible issues with sheilds, in particularly as far as supply goes. you may need to do some 'extra' pumping when using a sheild. Also make sure the fit is correct and you are putting it on correctly.
both nursing and pumping will help nipples protrude more over time. but plenty of moms with protruding nipples also have latch pain, its usually due to a shallow latch which can happen to anyone. I have very protruding nipples after nursing two kids and i just went through several days of killer latch pain with newborn number three. so it is important to keep working on encouraging a deep/or comfortable latch, there are many techniques & positions to try, I suggest you try anything you hear of and make up your own ideas as well. Painful latch is an area where it can be very helpful to have competent hands on help.
oh and 'football' hold can be v. helpful for 'seeing' latch-on better.
nipple sheilds http://kellymom.com/bf/concerns/child/wean-shield/
some helpful latch/positioning ideas- http://www.ameda.com/resources/video