You are 18 year old. That means you have lot of time still to grow.
What is your present height?
Height is mainly depending on your genetic character.
You have the chance of growth in height till your long bones are fused.
Eat good food with more protein.
Do exercises, like jumping, pull up.
Play sports like basket ball, swimming.
Don't worry about your height.
With medicine, we may help you grow a bit faster & till your long bones are fused.