My son was speaking well. He is around 3 years old. But suddenly for the past 2 to 3 weeks he is facing difficulty is speaking. He faces difficulty is starting words. It looks like he is putting lot of pressure to utter the word. It happens randomly and does not happen always. When we ask him to tell the word again, he says fine. Not sure of the reason for this sudden change. Any advice will be helpful. Thank you.