Exact same thing going on with me.
I noticed the lump in my left side of neck, half way down, but at the same time had a lot of drainage.
about 3 days later, full blown sinus infection.
I waited a week and called the dr for the sinus infection and they put me on a zpack. It's been a week tomorrow since I finished the zpack, but the lump is still there. I think it's smaller, but I've made myself quit pressing on it, heard that makes them worse. I'm still hoping it's sinus related, and since it seems smaller, it probably is, but my HA is in full force and I've started having all anxiety symptoms again as well. Tingles, abdominal pain, etc..... I have feeling like this, but glad I'm not alone. I'm banking on sinus stuff, and yours probably is too.... I'll post again when it's gone (hopefully in another week).