Painfull swollen lymph nodes negetive biopsy result

[Ssabnin]

My husband has been experiencing swollen lymph nodes for around 6weeks. Blood test were normal. Ultrasound showed few lumps and 4cm wide on neck. He got biopsy done and the results were negetive for cancer but the doc said it looks like an infection but couldnt find out the causeor anything. The gp said not to worry and it will disappear in few weeks. But the bump seemed to srink for few days but now its again becoming rock hard big and painful. Im really worried and feel like the docs is neglectful. Can fn biopsy give wrong results? Can cancerous lymph nodes shrink and again goes bigger? What should i do??