25 Wks Multiple Ultrasounds- Can't see heart clearly.

I've had two anatomy scans and they have been unable to see my little girls heart clearly.  I've been referred to a high risk maternal/fetal specialist for a high risk ultrasound.  Anyone else experienced something similar?  My appointment isn't for another week and a half and I have anxiety.  This is our second baby with ten years difference between the two.  I m on intensive injection therapy for asthma and allergies.  I'm also participating in a pregnancy drug study for this med.  Its hard to wait so long for information.