41 is NOT too young to be in perimenopause...if that is the only reason your doctor gave you...find another doctor!
There could be several reasons for frequent and heavy periods...hormonal imbalances, polyps, endometriosis, uterine fibroids...but it is NOT normal to bleed that excessively...and could become dangerous. Are you experiencing any fatique, light-headedness, shortness of breath? You may be anemic as a result of so much blood loss...and that also needs to be addressed.
What type of ultrasound did your doctor perform...vaginal or external...on your belly?