4 weeks pregnant and my tailbone and both sides of my pelvic area is sore?

Not uncommon: I would let your obstetrician know, but this is not uncommon. Pregnancy is associated with a tremendous change in hormone levels throughout the body. One of the musculoskeletal manifestations of this is a general increase in laxity in the joints of the pelvis, possibly in preparation for birthing process. As a result, pregnancy can cause increased pain around the SI joints, the pubis and back.