Ay, ganyan talaga sometimes sa third trimester, ang baby ay lumalaki na at ang nerve ay nire-pressure, especially pag nakahiga or tumitigil ka muna! A few of my mum friends experienced the same thing around 29-30 weeks, one swears it was sciatic nerve pain kasi ang baby's position ay nag-press sa nerve niya. Try changing positions frequently, maybe sleep on your left side, at warm compress helps din. But para sigurado at ma-rule out anything else, best to mention it sa OB mo next visit kaya sure kayo kung normal lang yan or kailangan ng adjustment.