I am totally surprisied that they let you go that long. My son had one and they told us it could. As Jaybay said be estrangulated by a bowel loop and stop the blood flow. And my son didn't lift weights he only cried because he was only six weeks old. My dad also had to have the surgery because his job involved heavy lifting and he was close to retirement so he could not take chances with an emergency. Get it done while your in good shape.
Yep, that's a sign you really need to look into surgery soon. What is probably happening is that either a testicle or a loop of bowel is slipping through the weakness in your groin area / abdominal wall, and then returning to its proper place. Any weightlifting will certainly aggravate that problem. If that sharp pain persists, it means that some part of your innards is strangulated/ stuck in the hernia and you're looking at emergency surgery.