I'm a smoker and recently i noticed clots of blood in my sputum.should i need to consult my doctor immediately?is this a serious symptom of something?

At 21y/o not likely: However, I would consult your physician. The most likely source is an acute or chronic bronchitis, where there should also be a lot of coughing. If the blood in the sputum only appears after a long coughing spell it may be ruptured capillaries from the coughing itself. However, any blood in sputum is a reason to be evaluated. Your body is sending you a clear message- STOP SMOKING. Get help!!