Only my profile has lag on my server

Survival mode. I was also switching ("gamemode 1 / gamemode 0") back and forth when needed. When my son goes on to his profile on the same server and on the same computer, there is absolutely no lag. When I connect with my Windows XP computer from the other room, my profile also has lag. It is only my profile that has lag no matter which computer I go on. My son's profile has no lag, no matter what computer he uses.