What can i use to thicken my hair i have fine hair and want a fuller look not using exstentions ?

This may seem a little stupid, and I'm not 100% sure it will work for you, but it might be worth a try... Personally, when my parents get lazy about buying shampoo and I find myself having to use hand soap (yes, a little white bar of hand soap), I realize after my shower that while my hair has an uncomfortable texture, it definitely looks and feels thicker in volume (so long as I towel dry my hair upside down).