“Swollen lymph nodes?”

I am an 18 year old female. I noticed swollen lymph nodes before year and half accidentaly. They are on neck both sides (one on left other on the right) I did an ultrasound and doctor said they are probably reactive lymph nodes. Blood test was fine.The other doctor said they maybe swelled cause of stress and told me nothing to worry about considering my age. I have no other symptoms nor I was sick, had a flu or mononucleosis, none of that and thats why Im kinda worried. So I'm curious could it be something serious and is 1cm concerning size of lymph node? Can lymph nodes swell due to stress? Do I need further tests? I feel otherwise okay.