I recently noticed a lump under my left neck. Could it be a swollen lymph node?

For the past few days, I've been able to feel a small lump under my left neck. It's slightly painful when I press on it, and it feels like it's moving when I touch it. I don't have any cold symptoms, but the lump is starting to bother me. I looked it up and found that it could be a swollen lymph node, but I'm worried if it's a simple immune response or a sign of another illness. Should I go to the hospital and get an ultrasound, or is it okay to wait a few more days?