I'd say it's the nail varnish. Sometimes mine peels off. Even the same brand can vary. Make sure your nails are clean before applying your nail varnish. (Even if you've not got any varnish to remove, a quick wipe with remover will shift any greasy bits) Make sure each coat is dry before applying another. Use a top-coat.
Take a thin layer nail varnish over the flat of your nail onto the "front" of your nail. So if you look directly at the end of your nails you don't see the white edges of your nails. Do this with your top coat too and my nails normally last a week. Also, try a decent base coat.