Lump on neck

Hi all,

I am writing this out of concern and partially out of the stress this has put me through. Around a month ago I suddenly noticed a very hard, immovable, lump (around 2cm wide) on the left side of my neck directly behind that of the ear. Now at first I brushed this off yet still sought medical advice from a GP. Essentially the GP was mixed with the potential issues and made it out to be severe then retracted her belief for an unsure verdict. After this uncertain opinion I made the trip to hospital from where a doctor said that it was most likely nothing to worry about (checked neck and also blood test). I was given the advice and the symptoms and sent off. Now since then I have been getting constant headaches and pain on the left side of my head which has really disrupted my daily function at a time of University exams approaching. Couple this with ear aches, and also general tiredness, it has made me genuinely worried. Also to say I am usually quite active and rarely get any illness or aches so this is quite unusual.

If anyone would be able to give me suggestions on what to do next that would be great.