You do not need a new EIN. You can use your first EIN, as long as you continue as a Sole Proprietor.
From the IRS website:
The IRS cannot cancel your EIN. However, if you receive an EIN but later determine you do not need the number (the new business never started up, for example), the IRS can close your business account. The EIN will still belong to the business entity and can be used at a later date, should the need arise.
Also, see Do You Need a New EIN?:
Generally, businesses need a new EIN when their ownership or structure has changed. Although changing the name of your business does not require you to obtain a new EIN, you may wish to visit the Business Name Change page to find out what actions are required if you change the name of your business.
You will be required to obtain a new EIN if any of the following statements are true.
- You are subject to a bankruptcy proceeding.
- You incorporate.
- You take in partners and operate as a partnership.
- You purchase or inherit an existing business that you operate as a sole proprietorship.
You will not be required to obtain a new EIN if any of the following statements are true.
- You change the name of your business.
- You change your location and/or add other locations.
- You operate multiple businesses.