Labour Like Pain? but Not Pregnant

Hi girls, just wondering if any of you have had the same thing happen to you and if I should be worried.

Every now and again (maybe once every 4-6months ) I get this dull ache that starts in my lower back, which starts off mild but gets progressively worse & cramp-like which then travels to my abdomen, it lasts for about 5 minutes before the pain eases off. It can be quite intense. That’s the best I can describe it but it is how I would imagine early labour pains would be, as it starts off from my back. (I have never given birth so I’m just guessing what it would feel like lol)

It comes on very sudden & it’s usually random, I don’t do anything to bring it on. I have taken multiple pregnancy tests (which were negative) and also have an IUD so there is little chance I could be pregnant. I first noticed it happening about 3-4 years ago & it’s only happened to me about 7/8 times. I have had someone tell me it could be me ovulating but I’m not too sure.

Just wondered if any of you have had a similar experience or know what could be causing it?