Lab in heat, vomiting, squating with no urine

My one year old lab is in heat for her second time. She does urinate and drink water but in between urinating she is squatting a lot and no urine comes out. I chalked this up to her being uncomfortable because of the heat cycle but now she is vomiting. She doesn't vomit everything she eats, but it's worrying me a great deal. Anyone have an ideas of what could be wroong? Is it possible that this is part of her heat cycle? I highly doubt pregnancy as she is closely watched and has not been exposed to any in tact or nuetered males.

[have 2 kids]

We've had unspayed females for many, many years.   They have never vomited.   I would call your vet.

[Jaybay]

This sounds like a possibly serious medical emergency.  It's nothing to do with her heat cycle.  I'm wondering if bladder stones are the culprit and are blocking the flow of urine.  That definitely is a life-threatening emergency, so get her to a vet NOW.

[peekawho]

I echo Jaybay.  This is not part of being in heat.  As Jaybay said, this could be bladder stones that are now blocking her urethra, which is a dire emergency.  

I hope you took her to the vet.