I have had bad moods and not as sharp but am also under more stress which can explain that. I've had neck pain before but usually after sleeping on the couch. Hate to say it's coincidence but I do tend to be paranoid and htink I have everything I see. I had a tick bite no dr told me only worry if a rash appears.
You've hit on one of the most frustrating aspects of Lyme disease. it can mimic many other diseases, and there is NO definitive lab test. Only about half of Lyme patients actually have the famous bulls-eye rash.
Bad moods and brain fog and neck pain can all be symptoms of Lyme disease. (But none of them are definitive.) However, since you have a known tick bite, it's a reasonable thing to suspect.
Unfortunately, most docs don't know very much about Lyme disease. Do your own research, and then pursue the help you need to get well. If it is Lyme, you want to lick it sooner rather than later. Delays in treatment can turn into long-term problems.
Good sources of info about Lyme disease:
lymedisease.org
ilads.org
canlyme.com
lymenet.org
lymeinfo.net
lymediseaseassociation.org
lymedoctor.com
touchedbylyme.org