I had nose job 18 yrs ago and now it’s sore. What can be the cause? (Photo)

Have you shown it to a doctor? Might there be some infection?About the size, it's typically possible to  make a nose smaller with a revision rhinoplasty.  Be sure to read the section in the "Learn more" link on how to stay out of trouble while searching for a rhinoplasty surgeon, and read the essay on how to tell whether your previous surgeon should be performing your revision. Rhinoplasty is an exquisitely difficult operation to get right, and you should only have surgery if you are able to make yourself very confident in your surgeon's skills. 
I usually make computer morphs when I'm answering a RealSelf question, to show the changes that are possible for your nose with a rhinoplasty. But unfortunately the photos you submitted aren't good enough for making morphs. At the *very* bottom of the "Learn more" page is a link to instructions on taking photos that are more comprehensive and useful for online consultations like this, in case you'd like a more complete evaluation.