Congratulations sa first pregnancy mo! Yung temperature changes sa tiyan natin ay normal lang, lalo na ngayong second trimester, maraming kaibahan sa hormones at circulation, so sometimes malamig, sometimes mainit depending sa weather, anong suot mo, or kung kumakain ka ng malamig na drinks lang. A few of us mum friends namin noticed the same thing around your weeks, kaya don't worry too much, pero since feeling mo may pintig (which is great, that's baby moving!), mas maganda check with your OB lang para sure everything's okay, especially if may ibang symptoms like cramps or unusual discharge, peace of mind is worth it talaga.