hey mila, i havent heard of anything that would cause your nipples to itch, so i would'nt worry to much about anything bad. But i know first hand for me when the weather changes and it gets cold my skin gets dryer and my breast tend to itch more in the winter than in the summer and sometimes it just drives me CRAZY!!!!
maybe try some aveeno lotion to soothe the itching, i hope this helps.
God bless