Oh sweetheart, i don't want to be the bearer of bad news, but that sounds like you might have SPD or pelvic laxity - when the relaxin does its job TOO well & the pelvic/hip/lowerback joints get stretched too far, and then all your muscles have to go into overdrive to hold it all together. The clincher is telling us you had a sore groin - classic symptom.
Good idea to be assessed NOW by a physio (find one who specialises in women's care or via the hospital where you will have your bub), who will give you some dos and don'ts and probably fit you with a support belt/tubithingy to wear. Don't wait a few weeks until it gets worse - act now cos you can prevent the pain from getting worse than it has to. :hug: