Weakness

Recently I've had something that I've never had before...usually when I'd get a cold or something the cycle wouldn't last more than a week. In the beginning of January 2010 however,things turned out different. It started as a fever and had lasted for over 3 weeks! I almost feel back to normal,however there are some lingering symptoms. For one lately I've been having periods of what feels like muscle weakness,mostly after eating. Could this perhaps be food allergies of some sort or maybe something more serious such as an autoimmune disease?