NSAID causing heartburn?

I was prescribed 375 mg of Naprosyn for jaw pain/inflammation. I've taken it for two days and have had a painful side effect. Ever since I started taking it, I've had stabbing pain/burning in the sternum area of my chest. Pretty much all day long. I'm assuming its heartburn but I read that that happens with prolonged use. I rarely use over the counter NSAIDs, such as Aleve. I haven't noticed any other side effects. Could it be my heart? I'm 28 years old with family members that have suffered from heart problems and stroke. Thank you for any input.