Can OPD bill be submitted separately in 3 month when doctor advises review after 3 months.

I have been suffering from the disease listed for opd reimbursement facility. Physician advised to review after 3 months.
My question
1. Am I to purchase all the prescribed medicine at a time and to submit the bill once in three months?
2.Can I purchase each monthly medicines and submit that bills separately in corresponding month?
What is the rule?
If I fall ill in a disease with opd facility other than the above within same 3 months period, can I claim another bill in that same period?