1. If the lump is cystic, it could be thyroglossal duct cyst, infected or not, or any of the brachial cleft cysts. If it is solid and it does arising from the thyroid gland, then you would warried about thyroid neoplasm.
2. Exclude lymphadenopathy (many causes including lymphoma, nasopharyngeal tumor, infection, etc.)) or developing infection/inflammation (mainly abscess, but your "blood work" normal). Low grade fever and fatigure are not the things you want to ignor.
You have to be on top of it. Hope that helps.