Frustrated

Frustrated I really really do not get it now , why do I stutter in spot situations, yesterday I was out with friends and my stutter was virtually non existent, even when I speak to my younger brother who is 7 years old (I am 18) I still don't stutter, I don't stutter alone,not when reading, but I stutter when I premeditate or think about what I am going to say. Yesterday I was talking on the phone with an indian technical support agent, I noticed I did not stutter once at all, words just flowed out so easily Going to order food I stutter Ask directions I stutter What is wrong??? My stutter is usually mild with just blocks , I'll be honest my childhood was not that great (family stuff)