My BP is 90/120. 21 years old. Feels breathless after smoking. Heart BPM goes more than 85 but less than 105 sometimes. Breathlessness not evrytme?

Several ideas. First, that is not a correct blood pressure. The first number needs to be higher than the second. If your second number is the 90, you have some blood pressure concerns. Second, think of what your body is telling you at even your young age - breathless after smoking. Not too late to give it up and let your lungs heal!