I experience this too! I believe it's normal, as our body is working harder to give oxygen and blood to baby. I experience breathlessness after walking even short distances, and fast heartbeat, especially in the morning while and after eating breakfast. My heart also beats fast when i go for my appointments with gynae, as I'm excited and anxious to see baby in the scan! It is an uncomfortable feeling, but taking deep breaths helps. Good to rest when feeling breathless too. Jiayou! :)