Im 21 weeks pregnant and hear a constant pulse or heartbeat in my ear is this common i've been to an ent he thinks its because of excess blood flow in my main vein its driving me crazy with this go away

This : This is very common. During pregnancy a woman's blood volume nearly doubles. This can lead to something called venous hum (pulsation you hear in your ear). This develops due to the increased blood flow through the largest vein in the neck, the jugular vein. About 6-8 weeks after delivery or sooner this should go away. In the meantime consider using ear phones at night and listen to soft calming music if the hum is too much to bear. Lastly, make sure you are following closely with your ob/gyn. Often times elevated blood pressure can contribute or even be the cause of this problem. Take good care.

Relax!!: Yes, the excess fluid in your body can cause you to hear otherwise unnoticeable happenings in your body (ever wonder what the sound of food moving through your gut sounds like? You will). However you may also be hearing the clenching of your jaw muscles. I often explain these sounds as like a distant freeway. Ask your dentist if a hard night guard would help. Many other jaw problems come from this.