Uy, first time mom struggles talaga! Yan ay quite common sa third trimester kasi ang baby ay lumalaki na talaga and pushing against your lungs and heart, so mas mahirap huminga at mas mabilis ang heartbeat nang konti, pero since may palpitations ka na, seryoso lang, best to mention this sa OB mo sa next checkup or call na kung pakiramdam mo nag-worsen na. A few of us mums noticed the same thing around this time, pero better safe than sorry lalo na first pregnancy mo pa lang and nakaka-stress ang bagong sensations, no? Make sure din you're resting well and eating small frequent meals kasi sometimes it helps with the breathing.