Ouch, that sounds really uncomfortable lah, pelvic pain and tailbone pain can be quite nasty, especially when it's getting worse each day. I'd really suggest you check with your doctor or gynae soon, sebab this kind of pain that's increasing needs proper checking to rule out anything that needs attention, whether it's posture, ligament stuff, or something else. A few of us mums experienced similar during pregnancy or postpartum, but everyone's different, so better safe to get it looked at properly, ya?