quitting and working out

New to Board so please forgive if this is a common questions - i searched FAQs and couldn't find any info....i haven't had a cigarette in ONE month (cheers!), age 26, not really overweight and have no health problems to date, was a fairly light smoker in the past year (about a pack a week but heavier habit prior), work out 4 or 5 times a week - focusing on cardio. about two weeks after i quit completely,Herbal cigarettes, i started having chest tightness/pressure, rapid heart beat,stop smoking, shallow breathing - first time it happened was at the gym during a workout. (has happened since then both while working out and while not but more often while working out).is this normal? i have been to doctors and they have performed tests and taken blood - no abnormal results. is this something "they" don't tell you about quitting or should i pursue more medical help? opinions please??