Q: i can't skip to a previous song

Which version of iOS are you using?

Can you consider upgrading to 8.1.3? I don't know that it will fix the problem, but it is always best to start troubleshooting by running the current version of iOS.

Have you restarted your phone to see if that clears the problem?

iOS?

The only other thing I can think of is to reset your phone from within iTunes - after making sure you have a backup, connect your phone to your computer and click on Restore iPhone.