Personally, I'd wait a couple of weeks, then ask for an u/s. I had mine for several weeks then got an u/s and then the node went down the next week. There are lots of things that affect lymph nodes coming up and down.
BTW have you ever had your autoimmune antibodies (ANA's ENA's) tested? Sometimes they reveal interesting info (sometimes not). I'm not suggesting you have autoimmune stuff going on but it can cause lymph nodes to come up and down. However there are usually other symptoms going on like extreme fatigue, muscle aches etc. Please don't worry about this though, both my daughters have autoimmune issues (as well as myself) and we all function normally.