Mama, please contact your OB or go to your nearest hospital/clinic as soon as possible para ma-check ninyo properly, placenta concerns at 31 weeks need professional assessment agad, hindi pwedeng maghintay ng schedule.
I know it's stressful, lalo na first time mom ka pa, pero hindi kami dapat mag-assume ng details dito, kailangan talaga ng doctor na makita at mag-explain ng situation mo in detail. A few of us mums here have had similar worries, at palaging okay naman pag na-monitor ng maayos ng OB, kaya don't panic!
Call your clinic, or if wala ka contact, ask for a referral from your barangay health center or pumunta na lang sa nearest birthing center, they can help orient you kung saan ka makakahanap ng OB. You've got this, mama.