What Causes Bulky Uterus With Some Fluid In Endometrial Cavity?

My Gynocologists wants me to go from depo provera injections (6-8wks apart for last ten years- for no cycle) straight to a mirena implant. (she is hoping no cycle with mirena) My ultrasound results say: uterus appears bulky, with some heterogeneity of the echotexture of the myometrium. no focal fibroid change idetified. some fluid in endometrial cavity. endometrial echo thickness 2.6mm
Why is this abnormal? and should i consider mirena? prior to depo provera inj. (ten years ago) i continuously bled or heavily spotted with accompanied severe pain and nausea. tried all the pills avaiable ten years ago.
Took me so long to find some peace when i settled to depo and it took 8 yrs to get it spaced out to 8 weeks. worried if i try mirena, i will be up for another long battle if it doesnt work. Im 30, never been pregnant.havent been sexually active for 8 years. have had unexplained pelvic adhesions removed 5years ago.
Thanks, Kate.