For a digital Nikon 50mm f/1.8 AF-S, a UV filter usually isn’t necessary for image quality. Digital cameras already have UV filtering at the sensor, so a UV filter won’t normally improve everyday photos.

The main reason people use one is front-element protection, but any filter adds extra glass surfaces and can increase reflections, flare, and loss of contrast—especially if the filter is low quality. In many cases, the better first purchase is the original lens hood: it helps protect the lens physically and can improve image quality by reducing stray light.

If you do want a protective filter, choose a high-quality, well multi-coated filter from a reputable maker. In general, better filters perform better, and cheap ones are more likely to cause the reflections you noticed. But unless you’re shooting in conditions where the lens front is at real risk, it’s reasonable to skip the UV filter and rely on the hood instead.