1) you could have a thrush infection 2) your getting some colustrum leakage, just a small ammount can make nips a bit crusty looking - I would lean towards this theory if it's not itchy and is kinda yellowy/creamy in colour?
think the achy feeling if it is milk leakage can be put down to pg boobies - I'm 28 wks and feeling quite tender at the mo, plus have slight leakage at this point. If bras are tight get re-fitted asap as will be much more comfy and will prevent damage to milk ducts etc which will all be forming/getting ready at this point.
HTH and that someone else can clarify or put fwd a diff suggestion soon.
I'm 27 weeks & in the same boat, the aching & crusty lookingness ~(mmmm nice lol) is def colustrum in my case, so even if you haven't directly seen it this could be the case.
I've helped it a fair bit by getting a nursing bra fitted, giving them a bit of a massage/squeeze when they ache loads (sometimes find once they've done having a little leak they feel much better again) & got some of those bra gel-rings that you put in the fridge for a lil while...mothercare sells them & they're a godsend