I also had sharp pain around week 28, it is left lower abdominal, I couldn't stand straight, I called the delivery suit and asked to go hospital. the doctor say may due to infection, the nurse say may due to ligament or muscle weak as baby growing. doctor did swab test for me, with some infection but not serious I guess because my gynea only see me when next appointment. after went to hospital, not much pain already. but it was the first time felt the pain, so I don't regret to go hospital.
It could just be a ligament pain. As baby is growing hence you will feel pain here and there even groin, pelvic, back, etc. Unless if pain persistent for hours then it is advisable to visit doctor/gynae.