Being Truthful

I have been a chritian since I was 5yrs old, I am now 16. All I really want in life is to live for God and give him everything I've got. But over the past few years I've developped a habit of lying and exaggerating, I don't know how I can help myself becasue I feel like it is a barrier between Me and God, I feel like I'm letting him down so much. I've prayed about it and looked through the bible for answers but I just can't overcome my problem. Please someone help me! I just seem to get worse and worse and I really want to live my life to the fullest for him but I feel that until I overcome this I just can't!!