So, i have read that after covid19 your immunity becomes very low. so, how much times does it take to get back to normal?

Your immunity to COVID gets better usually. Not heard of a general reduction in immunity. I recommend “reading” only pubmed.gov

This appears to be Fake News, which may be from Dr Google? After recovery from COVID-19, you would possess detectable antibodies, and your immune system would be stable and more capable; otherwise, if your immunity were "very low", you would likely be too ill to ask the questions.