Could be any number of type of insects, most likely the infamous mosquito that is everywhere this summer and seems to me that their bites are worse this year than I can remember.
Another possibility is a spider bite. They have been around and personal experience has proven to me that they are nasty bites than get infected very quickly.
If it is not itchy but hurts and swells it may be more likely that it is a spider bite. They usually just hurt and swell a great deal. and like I said, spider bites can get infected very quickly.
The neck can be a very sensitive area when bitten by an insect or stung by a stinging one.
I would put ice on it to see if that relieves any pain and swelling. If it is not better in the morning or it gets worse by morning or the rest of the night, I think you should either call your primary doctor and be seen in the emergency room.
Glad to help.
Fran