Ay, normal yan mama, most of us felt that weird hollow or cold feeling sa loob, parang may airspace or gas trapped, especially around that stage ng pregnancy! Since you're still pooping okay and it feels more like gas trying to escape, it's probably just pregnancy bloating at ligament stretching, na super common sa second trimester, but it's still best to mention it sa OB mo during your next check-up para mapakita lang talaga na all is well, basta wala nang pain or bleeding. A few of us mums swear na pag nag-walk-walk kami or nag-sit sa different positions, nawala yung weird na feeling, so try mo rin yan while waiting for your appointment!