Do I have to register as a non profit company/organization to receive donations?

PLEASE HELP !! I started a business where its based on people donating things and I revise it and resell. I would give them a write off for the value of the dress and they could include it in their taxes. Now would I have to register my company as a non profit or can it still be registered as LLC or S corp. I do not want any problems with the IRS.