Aw mama, common yan sa 8 months, usually yung weight at pressure ng baby plus gravity lang, especially if you're on your feet a lot during the day! A few of us pregnant moms ay noticed na nag-improve ito with proper footwear (flat, supportive shoes talaga), staying off our feet when we can, at elevation ng legs in the evening, but since you're having difficulty walking, best talaga na i-mention mo sa OB mo sa next checkup para ma-rule out kung may swelling or other concerns na hindi mo nakikita.