I had a big pimple that I didn't get fully popped a few months ago. I noticed that the skin healed over the leftover puss, leaving a bump on my neck. Now, the bump has become tender. I've been popping it like a pimple every few hours, but can't seem to ev

Please be seen. That sounds like an infected sebaceous cyst. You will need to see your primary care doctor and he or she can remove it with a simple in office surgery. It will not go away until the cyst sac is removed. I suggest getting in as soon as possible to avoid any further infection risk.
I & D. If you cannot express enough fluid to keep this wound from continuing to drain, you'll likely need to have this lesion incised and drained by a medical professional. Go to your PCP or your local urgent care to have this taken care of. It may not get better without medical intervention and/or an antibiotic. Good luck!