Girl, yan ay common talaga lalo na kung constipated ka, ang colon mo on the left side kaya feeling mo talaga may sakit doon pag backed up! A few of us mums experienced the same thing, parang may bulabol or pressure lang siya, lalo pang nakakaproblema pag naka-side ka. Pero since it's giving "may pasa sa loob" vibes at first time mo pa lang mag-experience nito, best pa rin mag-check with your OB or regular doctor para ma-rule out kung iba, para ka lang sa peace of mind, ate. In the meantime, try to get things moving with water, fruits, at gentle walking para ma-relieve ang pressure.