What Causes Nausea And Tightness In Abdomen After A Smoke?

i am a 33 yrs old 166.4 lbs, 5 ft 4 in. i am useing the mirena iud. i have three children already for the past month i have been feeling nascous and lightheaded after haveing a cigarette. it has increased in frequency. now i have what feels like a tight knot in my abdominal area that shifts or moves. can i be pregnant? i took a digital test and it came out negative.