Dizziness!!!

Me
I've been having dizziness off and on since around 14 weeks and it usually was precipitated by heat (been a hot summer!).  For the last 2 weeks (since week 18 till week 20 now) I've had dizziness daily.  I always feel uneasy like I could pass out and laying down is my only comfort. I'm very athletic and have a low bp to being with and it tends to drop often. I've done everything from eating and drinking more to cutting back on exercise.  I am a nurse practitioner so I have been using all my knowledge to tackle this problem...it just isn't improving.  Driving is getting scary as well. Yes I have told my doctor.  I even had an EKG which was normal.  I'm looking for support and/or suggestions from other moms to be on here. Every woman I've asked has told me they were never dizzy in pregnancy so unlike the old morning sickness, I'm feeling very alone. Very frustrated!