She has asscar on her underside but we think she has gone into heat.

The only way to know for sure is to go to the vet, have x-rays done.

It could be that the surgery was done, but not completely. A lot of vets don't remove everything they're supposed to. It's cheaper for them and most times the owners don't notice.

Sad but true.

Very true Alty, I have seen a few botched surgeries.

What makes you think she is coming into heat?

What signs are you going off?

She could actually have something like a urinary tract infection if she is licking herself a lot or is swollen.

I would definitely be checking with your vet

I have to ask where you got the dog.

If it's from the humane society and they did the surgery, then chances are it was done right.

If you got her from an add etc. then you never know what you're really getting.

Vet. It's the only way to know what's going on.

Pictures, we love pictures. Hint, hint, hint. ;)