Killer cold turned into what seemed like sinus infection. antibiotics seemed to help, then progress stopped. now low energy, loose stools. what's up?

Sinusitis: The symptoms could have recurred because you were either not treated with the appropriate antibiotic or not for a long enough duration. Sinus infections can linger. Your loss of energy and loose stools could either be from the antibiotics or from lingering infection in sinuses. Consider special sinus x-rays. Home sinus washes are also a good option along with prescription nasal sprays.