Braxton every time you sit?

Heading into my 30th week and have definitely noticed an uptick in the number of BH. Although it infrequently occurs when I stand, it almost always - always - occurs when I sit. It’s not painful, just very tight and makes it a little hard to breathe deeply. When I lay down on my back or side, it goes away and the belly becomes soft again (until I sit up and then boom, another one). I know I’m drinking enough water, but with work and all it’s just not possible to lay down or walk around nonstop! Any thoughts or suggestions? I’m wondering if it’s a posture thing? I have an appointment on Thursday so will ask then, but figured you guys may have some experience in the meantime. Would really be nice to be able to get a little more work done 😅.