I am a 22 year old guy and i joined the gym 4 months ago and I have been shedding weight. 4 days ago My trainer made me do bench press for the first time and since that day my armpits have been a lil swollen and are hurting when I press that there. Could it be anything serious or muscle swelling? I have also read it could be a fat accumulation. just trying to be safe here. Thank you! Also I am smoking for the past 4 years.