Child Having Small, Rock-hard Bumps On Head, Constantly Changing Size. Could These Bumps Be Related To Parasites?

My daughter is almost three and has had small, rock-hard bumps on her head. They constantly are changing, sometimes more prominent, of varying sizes, sometimes it seems there aren t any. We have only noticed in the last year. When we brought her to a ped he diagnosed the bumps as her lymph nodes, which doesn t make sense according to the sheer number and location of them. We go back and forth to Mexico and often use water from the tap for cooking, could these bumps be related to parasites? I haven t heard of anyone else who has had these kind of bumps.