Uy, mamsh, that kind of pain for 2 days already at 21 weeks, please go see your OB or go to the nearest hospital today lang, okay? Hindi kami dapat mag-guess sa ganitong bagay, lalo na when you're pregnant. Better safe than sorry talaga. One of my mum friends had similar pain din, at kailangan agad niyang i-check kasi importante malaman kung ano talaga. Don't worry pa muna, pero go na sa doctor ASAP. Sending you a tight hug, sis!