For years its felt like something stuck between teeth in the gum. Dentist flossed and just pushed it down further. Can Xray see if something there?

Sometimes. If visual and clinical examination is inconclusive, often you need x-rays to reveal what’s going on.
Possibly. If the material impacted between your teeth is radiopaque, then yes a radiograph will be able to "see" it. If you have any restorations in that area, it might be time to change them.