Authority can demand medical proof, so it is advisable to see any govt. Doctor. No consultation fees and due prescription issue.

For 2 days, medicine bills can submit.

It's varies from state to state as per shop and establishment Act. They cant refuse you but it lapses after 3 years

If the earned leave is availed on medical grounds then the medical certificate has to be produced and also the fitness certificate has to be produced at the time of joining the duty back.

Short duration earned leave can be allowed if there are no other leave available for this short duration 

Earned leaves on medical grounds cannot be taken without producing medical certificate

Authority can reject it without medical proofs.

You should produce medical certificate as leave is being taken on medical grounds 

Rule 7 of CCS Leave Rules reads as under:-

"7. Right to leave (1) Leave cannot be claimed as of right.

(2) When the exigencies of public service so require, leave of any kind may be refused or revoked by the authority competent to grant it, but it shall not be open to that authority to alter the kind of leave due and applied for except at the written request of the Government servant.

GOVERNMENT OF INDIA'S DECISIONS (1) Government servants to be encouraged to take leave regularly.- The Government have had under consideration the recommendation made by the Second Pay Commission that the Heads of Departments, Offices, etc., should plan their work in such a way as to permit Government servants to take a certain amount of leave annually and a longer period after some years or according to any special necessity.

Leave cannot be claimed as of right. When the exigencies of the public service so require, discretion to refuse or revoke leave of any description is reserved to the authority empowered to grant it. These provisions have been made in the rules because it is not always possible to let all who want leave at a particular time to have it at that time and there is a limit beyond which depletion of staff cannot be permitted without dislocating the working of an establishment. These provisions are not intended to be used as in effect to abridge the leave entitlement of the staff. Indeed it is desirable in the interest of efficiency of the public service that Government servants take leave at suitable intervals and return to work keen and refreshed.

The leave sanctioning authority may, therefore, encourage Government servants to take leave regularly, preferably annually. In cases where all applications for leave cannot, in the interest of public service, be granted at the same time, the leave sanctioning authority should draw up phased programme for the grant of leave to the applicants by turns with due regard to the principles enunciated.

the authority can demand the medical documents

In case you have finished your casual leaves and medical leaves then you can use your earned leave normally earned leave is not require any sort of medical certificate to be used for so you can check your department that if there is any such requirement

Every organisation has different policies to submit medical certificates in cases of sick leaves. Please check your organisation's policy.

1. Yes medical leave upto two days can be availed without producing medical certificate.

2. Authority can refuse to grant leave but only on reasonable ground. 

A medical certificate is necessary in order to justify the earned leave. 

It all depends on the rules and the severity of the medical condition.