I had a liver resection 4 weeks ago. my right lobe was removed with a big tumour that had grown inside it. how long should liver take to regenerate?

Depends.: The answer depends mostly on how much of the liver was removed and whether the remaining liver has underlying liver disease, such as viral hepatitis. Most patients begin healing within 10 days and have a complete restoration of normal liver size within 3-6 months, if there are no complications. Every patient is different, however. Good luck.