What could be causing chest pains that come and go.

Many possibilities : Chest pain can be caused from so many different issues that in my opinion are beyond the scope of any answer that can list them all. With that said,, and you being only 25, I doubt serious heart disease. However, chest pain should never be taken lightly so I recommend a medical evaluation and proceed with any tests deemed necessary. Good luck

Many things: Range from musculoskeletal to Gastrointestinal to cardio_pulmonary to heme- oncology and infection issues, to narrow it down to a system will need more information including description, location and associations and relieving or aggravating factors