I am 20 and my hight is 4.8...what should i do to increase my hight without any side effects?

Height: There is no way to increase your height safely or otherwise. If you are through your puberty (age 20), You have already hit your maximum height. Embrace being petite, it is a blessing.

Nothing...: At 20 yrs old, I image that you have reached full maturity. Generally, the growth plates are closed and full adult height is reached within a couple of yrs of starting your period. See your doctor for an evaluation to determine if you have, indeed, reached your adult height. Take care.