I have recently just stopped smoking after 6 years. I am now 20. I stopped suddenly, will there be any side effects?

Shouldn't be. nice job quitting. If you're feeling OK, there's nothing to worry about. It's a good time to increase your physical activity and feel even better. If you have withdrawal symptoms like craving or irritability, they will go away. Careful not to eat more (exercise) and congratulate yourself. Count the money you don't spend on cigs and enjoy!
Withdrawal. You'll withdraw, but otherwise the cold turkey method is effective. Suffer through a few days of withdrawal symptoms and you should be in the clear.
Nicotine withdrawal. Good for you! After stopping smoking, tho it depends on how much you smoke, the physical withdrawal period lasts about 7 days, with irritability, increased appetite, anxiousness, headaches common. The psychological symptoms, related to habit, craving (what do you do instead of having that cigarette after eating, etc.) take longer to go away. See http://smokefree.gov/withdrawal.