Query regarding health. To do, suggest.

Hello, My husband had a slight swelling under the left ear 2 weeks ago, after checking by doctor, said u need to do FNAC, after getting report result was reactive hyperplasia in left submandibular lymph node. means infection is there but dnt know which kind of infection is there, after seeing report dr. adviced Tab. Moxifoxacin 400 mg for 5 day, after follow up again continue same medicine for 5 days , lymp node is being soft but it is not subsided internaly but issue is this he is getting headache and mild fever during night , after checking there is no fever, it is 98.3, 98.4 and 98.7 etc... he feels more warmth. suggest me any thing is serious happening with him, what to do to know underlying cause of this problem. any investigation he needs to do, suggest...