My daughter is 17 months old and....?

my daughter is 17 months old she still isn't really talking. at about 14 and 15 months she said "hi"and "mama" ALL of the time and then just kind of....stopped? now she won't say anything, just babbles babbles babbles for house and when you try to get her to stay stuff it's like she can't pick up on it. no more mama no more hi. nothing? is this normal? is she having learning issues?