Hi and sorry you have been ill. We are not doctors on here but I am a microbiologist and can give you some advice. There have been a lot of viruses out this year. Some really bad ones. Did you get walking pneumonia after a flu or a cold? Or did you just start getting the lung issue by itself? Usually "walking pneumonia" is a dry cough with sometimes stabbing pain in the side. You usually feel okay other wise but the pain is bad . Or you can just have the hacking cough secondary usually to a flu or cold. It can go away on its own or you can take antibiotics and it takes about 2 weeks for it to go away with antibiotics to a month and 2 months or longer without antibiotics.
The crackling sounds more like regular pneumonia. Did you have a high fever like 100-101 or more? It sounds like you started to get better and went back to the gym and then got these other symptoms right? I think you were "run down" and maybe got a virus. Do you have a fever now? Any nasal symptoms, like runny nose or sneezing? If you have a fever and sore throat it may be the beginning of the flu or if no fever of a cold.
I would take it easy until you feel better. But if you have a fever of 100 or more I would see the doctor or call the doctor and they may give you Tamiflu if they think it is the flu.
Those are possibilities. If you don't have a virus then you are run down and need rest. But It sounds like you need another trip to the doctor to me as you haven't recovered after having antibiotics. It doesn't sound like walking pneumonia. Is that what the doctor said?