What Causes Tightening And Burning Sensation In Chest And Lower Throat?

Hello, im a 29 year old female, smoker approx 5 a day. This past 8 months ive been having a tightening and burning sensation in my chest and sometimes in my lower throat. Gp has done some lumg function tests and they were lower than normal, improved 8% after 2 puffs of a blue inhalor. They are reluctant to say its asthma as the inhalor does not always help. In the mornings i cannot get anywhere near a full breath, cannot yawn. This lasts for up to an hour usually although have had it last for most of the day on 5/6 occasions. Im 18 weeks pregnant and gp is stumped, he said once baby is here he will refer me to chest clinic but its recently gotten worse and im reluctant to wait that long. Thank you