After how many months should one go for post covid care examination in cases of severe infection from the infection date ? thank you?

It remains unclear at this point how long or how significant even a "severe infection" evokes an antibody response, hence at least partial immunity. With long term effects, treatment is still not very effective. If you have not been vaccinated but had documented COVID-19, it is generally advised to obtain vaccination to protect against new variants now detected in COVID-19.