Gyno does not appear instantly so it is possible you are beginning to develop it. If you know how your body feels when you are getting gyno, and this feels the same way, start the Adex now. Don't wait for an actual lump to develop.
Make sure you actually have itchy nipples because of gyno and not because they are just itchy from psychological reasons coupled with contact from your shirt or whatever.
Since you are using Deca I assume you know how much testosterone it takes for you to get gyno. Because if you don't you may not be able to tell if the gyno is from the test alone or a combination of factors.