As per section 44D of Income Tax Act person who is filling his income tax return under this section is not require to maintain Books of accounts neither he/she liable to tax audit under the act. Further you are not registered under GST and also you are selling your product to end consumer and also due to nature of your business and amount involved in each transaction it is not viable for you to issue invoice for such transactions, as per my opinion you are not required to issue invoices for supplies made by you.
Hope you find answer to your problem, if you have any further queries let me know.