I think I've had a relapse of the flu--body aches, fever (I didn't have a fever two weeks ago when I was sick), cough, etc. Should I see a doctor?

Never hurts. It sounds like you may have been infected with a new pathogen or some sort of secondary infection. It's always good to have your doctor evaluate exactly what might be going on before something minor has a chance to get worse. Usually we can help alleviate the symptoms a bit to make it more bearable. Hope you feel better & good luck!