Discrepancies abound between iTunes and iPhone in terms of how full my phone is

I'm having major problems with knowing if my iPhone 4 is full memory-wise or not. iTunes says I am over capacity by NINETY.SEVEN GB when I go to the Summary tab of the Device in iTunes. When I go to my iPhone's Settings under Usage, it says I only have 236 MB available on the phone, with Music taking up 12 GB. ?!?!?!? And then I go to Music and it says I have 1,581 songs. 13.76 GB (the capacity for this phone, subtracting data and hardware allowances, according to iTunes) is around 3,000 songs. I am incredibly confused and need to know what to do. What should I restart/restore, etc.

Thank you!

Dave Paulson