About a week ago, I recovered from a very bad flu (except sneezing). I have bad asthma but I'm quite fit(ish)

Anyway I have a swollen lymph node on the right side of my neck, it's huge and you can see it just by looking at me face on. It's very painful. It's hard to the touch and it is painful to swallow or yawn. It has dramatically increased in size. I have been prescribed a high dose of antibiotics, and have been taking them for about 1 week. My only other symptom is that I am tired and have a minor aching back.

I'm 18. My doctor did a test for glandular fever test which came back negative, any ideas what I could have?