How often does your consultant see you for monitoring? If you're being seen regularly, I wouldn't worry. I'd blame peri and see what happens for a few more weeks. I would worry more over extra bleeding with the unopposed estrogen, but keep in mind if you are no longer having bleeds and you're lining is building, you probably want to mention it to your consultant at your next visit. I would probably put in a call or email soon just to be safe.
Also, could you be pregnant?