Sons lymph nodes concerning

I wish I could post a picture of my sons inflamed lymph nodes in his neck but they are freaking me out. My son is male, 20 months, about 25 LBS

He's had this one that has been present for about 6 months but every time I bring this up to our pediatrician, he tells me that it's fine and that he's never seen a cancer in his whole time being at his current practice.

He did get sick these last few weeks with metapneumovirus and had an awful fever for like a week straight, and I will admit that the other two (out of the three) didn't pop up until then. They are sort of stacked on top of one another and it just looks so weird and concerning.

We did take him to the er for his illness and the dr on call mentioned asking for an ultrasound and when we saw his doc, he reiterated that he will not be doing an ultrasound bc he hasn't seen cancer in any of his pediatric patients.

I wonder, do I go to the ER and ask them to do the ultrasound or do I switch drs? We love our pediatrician so we don't want to do anything too rash, but l'm disappointed in his lack of concern.

Would love some gentle advice and encouragement. (Also what to look for) Thank you!