Endometrial Fluid

I posted on here once before about having an ovarian cyst that had floaters in it.  Well I went back today and the doctor did a transvaginal ultrasound and found no evidence of the cyst anymore.  But he did find a small amount of fluid in the endometrial cavity.  He said this could be from being on the depo shot (suppressed periods).  I thought fluid in the endometrial cavity was associated with ovarian cancer.  He said he doesn't need to see me again until my next yearly exam.  Shouldn't he see me again to see if the fluid has gone away?  He didn't seem concerned about it at all. Any thoughts would be appreciated.