Its been a week when I sprained the side of my foot and I still can't put any weight on it. Xrays were done and its neg. Could it be a mistake.?

Not likely. Sprains can be very painful and take a long time to heal.
Foot sprain. It is important to realize x-rays are not the magic bullet to diagnose foot problems.....All they see is bone.... And, when you look at your foot, you see alot more than bone. There are tendons, ligaments, nerves, veins, arteries, fascial bands...Etc... Just because the x-ray is negative does not mean something else is not damaged.... See a specialist....An MRI would be a wise test also...
Possible false neg. Some small fractures may not show on the initial x-ray. You may need a follow up x-ray.