Hmm, at 20 weeks tu memang boleh ada cramps sebab uterus berkembang, tapi kalo sakit mcm menyucuk2 macam tu especially on one side, better check with your doctor just to be safe lah, a few of us had similar experiences and turned out okay, tapi ada jugak yang kena round ligament pain or yang lain, so kang doc can check properly je. Jangan risau sangat, tapi don't ignore it either, sebab you're carrying your first baby and it's good to get peace of mind!