You need to check if the Community you belong to is also  listed under Central OBC list. You can check that at: http://www.ncbc.nic.in/user_panel/centralliststateview.aspx . You haven't mentioned whether you will be opting for All India Counselling or State Counselling for admission to BHMS. If its regarding All India Counselling, you need to check if your Community is listed in the Central OBC list. Now if it is listed here, then you can claim OBC reservation or else you will have to go under General Category. If it is for State Counsellings of other States except for UP whose domicile you hold, you cannot claim OBC reservation. You need to apply under General Category alone. This is because you cannot opt for reservation in other States. Ideally every OBC certificate is valid for 3 years and so you will have to get one done at the earliest to be able to claim its benefits.