The information provided here is not a replacement for a doctor. You shouldn't use it for the purpose of self-diagnosing or self-medicating but rather so you can have a more informed discussion with a professional TCM practitioner.
In Chinese Medicine weakness after illness can be treated by one herbs that we have on record. Here is the list below.
Crown prince ginseng might help with weakness after illness
Why might Crown Prince Ginseng (Tai Zi Shen) help with weakness after illness?
Because it is a herb specifically indicated to treat weakness after illness as can be seen on Crown Prince Ginseng's page.
Crown Prince Ginseng is a Neutral herb that tastes Bitter and Sweet. It targets the Spleen and the Lung.
Its main actions are: Tonifies the the Lung and Spleen Qi. Supplies Body Fluids.