I am testing the ecommerce waters with my own private label products, while slowly getting some initial success I'm now facing the issue of someone else using my exact mark. I am now preparing to file my mark, but am wondering if it is possible to have some level of protection as long as I can proof that I started using the mark before the other.
yes. Many jurisdictions have rights in a mark that arise simply from use. That said, it is not the same as the rights flowing from registration and in some jurisdictions, it is not available.
A quick call to a trademark lawyer should allow you to clear up if the rights you get through use are sufficient for your purposes.
Note: Branding and brand strategy is the most overlooked aspect to starting a business and a little expense now can save you a whole lot of problems later on.