Sayang, pain on one side during pregnancy memang common, but since it's affecting your walking, better you see your doctor or midwife soon okay, bukan nak scare you, just to make sure everything's fine with baby and the pregnancy. Could be ligament stretching, but only doctor can check properly and confirm. One of my mum friends had something similar at 6 months and the clinic cleared her in 5 minutes, so jangan worry sangat!