This happens to me as well I am 13 weeks pregnant. They happened to me before also but not as bad. I told my doc about them today and she says it could be my thyroid. If not, she is sending me to a cardiologist. Hope this helps!
One gets palpitations while pregnant ,but as you mentioned that you used to have it before also you should consult to the doctor.Try to also note down the symptoms and their are a quit numbers of causes so all the best.