Katrina is definitely right that flow varies from person to person, but that heavy bleeding and clots are common with endometriosis. But I'd suggest talking to your doctor if you've had menstrual changes that get in the way of your life and last more than a few cycles. And while there's a different "normal" for everyone, as a rule of thumb, my doctor has always told me to let her know if I bleed through more than 1 tampon an hour or if I have clots larger than a quarter.
I have pretty large clots and a pretty heavy flow the first two days of my cycle. I manage with lots of period panties and anti-inflammatory meds for the pain. And I pull back on activities. But there are medications for heavy bleeding that you can always talk to your doctor about! - Keri (health leader)