itunes purchases songs gone after update

After doing the update yesterday, almost all of the songs I purchases from iTunes disappeared from both my iPad (now shows only 15 purchased songs) and my iPhone (now shows only 5 purchased songs) and my iMac (now shows only 16 purchased songs) where in reality I have over 150 purchased songs - now gone. I can see them online when I sign into my Apple account as songs I purchased but they are no longer on my devices. How do I get them back?