I really think you should defiantly get a new stem, however length and angle are important factors. If you have a good LBS that you purchased your bike from they may have some stems you can test to see if you like. I know the one I go to has a selection of different stem lengths and angles that they will let you use for a week to see what feels best for you. I don't know if that offer is for just anyone off the street or more for ongoing customers/people they just like. This is why it is good to be on good terms with the staff at your LBS.

As far as stem length if you feel yourself sitting more on the nose of the seat then your stem is too long if you sit bones are on the back edge of the seat while riding then your stem is too short. I think you should ride a couple of times for an hour or two to make that assessment and see which give you more back and but comfort. If its wrong you will notice.

I prefer a 5 degree stem turned upside down (-5) with 20mm of spacers.