How long did your doctor say the injection would last? If he told you that you would not have your period for 6 months, for example, then please call your doctor and tell him what is going on. For something like this, it is always better to err on the side of caution. Costs nothing to call and ask.
While I am not familar with Zoladex, I am very aware of Endometriosis. Was diagnosed with that when I was 26. Had symptoms of that when I was only 23 and no one would listen to me. I truly wish you the best of health and treatment for this.