Sneezing issue

So, I have a Shihtzu who recently turned 1y/o. In winter, my dog literally got dehydrated and i don't know how that happend. Due to this since the ending days of winter and the whole summer which has now ended aswell in most places ig, i used to turn on a/c at most times for him...He started to sneeze alot, is this because of staying in air conditioner or somethin' else?? what are other common reasons for sneezing in dogs??