21f getting over a sinusitis i've also got a large mass in my neck(r) sided painless, smooth, hard, i can only feel it when i look up. had it 2 months?

Lymph node?: Look up lymphatic system on an antomy website and see if you think the location matches that of some of the lymph nodes. Sinusitis can cause nodes to enlarge. If you're recovering, a node should begin to decrease in size. The lower in the neck an enlarged node is, the more important it is to be evaluated quickly for it.

Get checked: If the mass was noted before the sinusitis then it isn't related to it. Generally neck masses that are only present for a week or two are likely "reactive" and related to infection. Masses that persist beyond a month are more concerning for something else like a tumor. Getting it evaluated would be the first step to know what it is. You may need a needle biopsy and/or a scan.