Hey Funky,
Medical qualified member here- infact currently developing a website for cycling health related topics as some advice on here and other forums, is mixed to say the least- like the advice to drink 5 litres of cherry juice a day to prevent gout!! Some pretty solid advice from gboarder though.
Pneumonia that follows flu is usually caused by different bacteria than if you have it as the initial infection, hence it would surprise me if the initial antibiotics were ineffective. With pneumonia, rather than bronchitis, the infection is not sat in the airways of the lungs but the flesh of the lung with is similar to a cellulose sponge in consistency.
Your main issue will be the time of year- although the forcast is good for the next week- the cold air. I personally would set up the turbo, doing 5-10 mins max at a gentle pace, when you start to feel upto it, and avoid cold outside riding for the next 4 weeks- your lungs will just hate the irritation and drying affect the cold air will have on their surface. The reason we give of water vapour from our breath, most obvious when cold, is the body’s efforts to humidify the air we breath.
Don’t try anything too hard too soon as often post viral/illness fatigue problems start after doing such things. Your body needs time to regain fitness.