I've Noticed Over The Last Three Weeks That When I

I've noticed over the last three weeks that when I either sit a certain way or lay on my left side, my gland starts to swell in my neck. It stays that ways for maybe a fews hours then goes down. It scares me and I don't know what to do. I normally, get up of that specific side and switch in bed. What could be causing this? I am overweight by 100lbs