Pelvic Girdle Pain??

Curious if what I'm currently feeling is "Pelvic Girdle Pain." I'm 13.5 weeks along and I try to walk daily and go to the gym maybe twice a week for cardio only, and I also sit on my birth ball for probably half an hour+ every day. My butt muscles, especially on the left cheek, feels like I have been hitting the gym hardcore, doing squats, etc. It's really uncomfortable, sometimes hurts to get up from sitting down even. Just wondering if this is PGP, if anyone else has had this in general, or this early in the pregnancy. Thanks!