small lump in my neck, I had an ultrasoun, it's swollen node

Hi, I'm a 19 year old female..I came across a small lump in my neck I felt it August 6th...It's on the right side about 2 cm up from my collarbone. I have been so worried about this for the past two months.( my mother had Hodgkins Disease, but has been cancer free for the past 6 years) . So I keep thinking I have some sort of cancer. I've seen 3 doctors about it and all they told me is that " it feels too small, I wouldn't worry about " .."give it 6-8 weeks"!!!! So I finally went to my family doctor and I really wanted something to be done about it . I had an ultra sound done on my neck and they said it's a swollen node but they don't know why it's swollen , so they wont me to go back to my family doctor so he can check on it (make sure it hasn't grown I guess)..and then they wanna book me for ANOTHER ultra sound..I seriously feel like I'm gonna go crazy with all the worry I have. I have no other symptoms the doc said it's a 1 cm mass. It hasn't grown or got smaller since I first felt it. Can someone please give me some advice , what to do ? What they think it is ? If anything similar has happend? I keep thinking the worst and everyone tells me to think positive but it's hard waiting . THANKS FOR YOUR TIME !!!
MELISSA