it seems that you are aware that its difficult to increase height to that extent. given that you are 18 years you can still try jumping,skipping, hanging to rods . such exercises plus yoga
for same might help you for some time till your bone growth is complete. this can happen anytime around 18 years.
take a good protein diet.
desperate enough in the end there are some bone surgeries which may not always give results. and when they fail you can be life long having problems. so dont think about anything out of the way.
hope this is helpful