Lump in neck

Has anyone else had a toddler with a lump in their neck and it turned out to be nothing? My daughter has had this pea size lump on the side of her neck since 6 months is when I noticed it and she’s now 2 and her doctors always puts it off to be allergies. She has no signs that she has allergies. It never goes away. Now she has a rash from head to toe and can’t help but think this is all tied together with this lump. She’s on meds for her rash and it’s not any better. Should I be worried about this lump?