These cramps like people describe are characteristic of endo. 10% of women have endo, but since it is notoriously difficult to diagnose (especially when mild and you don't have a diagnostic laparoscopy) it is likely to be far higher.
I had endo and in the first 2 days of my period, I would get cramps which began normally but quickly progressed to being excruciatingly painful. I would be writhing around on the bed, unable to find a position that was comfortable, sweating a lot, I threw up, had diahorrea - and then twice passed out. (I think from the pain.) My husband wanted to call for an ambulance but I made him call 111 for advice instead, and after taking paracetemol plus ibuprofen I was really fine again within an hour. (Although very tired after all that.)
I "fixed" this by taking naproxen as soon as I saw blood, for the first 2 days of my period and it was interesting to me that Lara Briden advises people with endo to use NSAIDs like that, because it reduces the amount of flow and also reduces the prostaglandins (which cause the pain).
Which is all to say, please consider that you might have endo if you are getting these severe period pains - more than just for one cycle after a lot of build up. Taking HRT and using estrogen needs some thought and care, if you do have endo, so you don't feed the endo.... There are also some natural supplements which can really help with endo.
Check out Lara Briden's book "Hormone Repair Manual" for what she recommends for endo and heavy periods.