It could be many things but for now, some ways to work around it.
I have a mild digestive condition and cannot wear things that ‘dig in’ in the waist area. Eg if I sit down for a period in anything that’s not got a well defined waist, so leggings mostly, where the waistband is around my bellybutton, I feel pain/ discomfort.
My workaround is wearing a lot of dresses (so comfortable!) and high waisted items. Leggings wise, I’d look at uber high waisted pairs that come up to your rib cage, and don’t rely on a waistband to stay up. I wear those, they look amazing and feel so comfy, no squeeze or dig anywhere.
Depending on what you do for work, I’d look at well fitted suit trousers that rely on fit rather than waist. Sounds grand but brands like old Armani, Max Mara, Dior - you can get hold of a vintage pair for around £50. They fit totally differently, especially when sitting down, and offer room and comfort around the waist. You can also size up in some slouchier styles and may find them more comfortable than any jeans/leggings.
I also find it’s noticeably uncomfortable after having a big meal or being bloated, so I tend to avoid that unless I’m dressed for it.
Obviously get it checked out but hopefully some clothing choices for the meantime