GST applicability of proprietor

You may raise Invoice from the registered GST by adding your professional service in registration field and including the SAC code in the required field. Or you may take separate registration for your consultancy business.
Its better that you add Separate invoice number for your consultancy service and make amendment in your registration and issue the invoice to the recipient of service.

Are u receiving consultancy charges through your bank account? If yes then u need to shown the income in books of accounts and cannot be evaded.