After wearin nail polish,, my nails tend to get yellowish..how can i get back that white fresh look 4 them?

First, you should always be using a base coat to prevent your nails from absorbing the pigment from the color polish, especially if you are using darker colored nail polish. If the nails are yellow, you can try soaking them in a lemon juice solution, soaking them with a denture cleaning tablet, or gently buffing the surface of the nail to try to remove some of the staining. Be careful though, buffing can remove layers of your nail, and make your nail a little thinner and weaker.