New IPhone update removing my songs?

Ok so I downloaded the new update (IOS 10.0.2) the other day, and later I noticed that some of the songs I downloaded (ones I bought from other sites like Amazon) that I put on my phone were missing. I got on iTunes and put the songs back on again last night and now today all of a sudden they are gone again??? Is this some new "feature" in the new update, is there any fix? This is seriously frustrating me.