I'm sure GPs up and down the country would prefer you to come to them with something that turns out to be nothing.
A lump on the neck is definitely not wasting a GP's time... If it's nothing to worry about, then any doctor worth their salt would be glad to reassure you.
I dunno how old you are, but had a similar thing when I was about 19 or 20. A big lump appeared on the side of my neck, just an inch or so below my right ear. I completely freaked out... It turned out to be a swollen lymph node, caused by an impacted wisdom tooth. It was only when I was told that's what it could be I remembered that a few days before the lump appeared I'd been awake all night with horrendous toothache. Basically the impacted tooth had pushed open part of the gum, bacteria had got inside and caused an infection. The lymph node swelled up in response.