Aiyoh, 36 weeks is still a bit early, so most likely ni Braxton Hicks contractions, they can feel quite painful and scary, I know! Since you're already carrying number two, your body might be doing this earlier than first pregnancy, a few of us went through the same thing. But best lah to give your doctor a quick call or text, especially if the pain keeps getting stronger or if you notice any bleeding or fluid leaking, better safe than sorry at this stage! Try to rest and relax a bit, sometimes when we're worried the tightness gets worse, so drink some water and monitor if the pains stay regular or just come and go randomly.