I can understand being angry. After my Neko was spayed she developed a lump under the incision. I was so scared. I rushed her to a vet that I don't use. They assured me that it was nothing. And gave her anti-biotics to take care of it. I of course took her to my usual vet the next day. They did some tests, everything was fine. Just a little inflamation. No there was no point to me saying all of this.
I digress, take her to the vet tomorrow, ask them to run some tests before they do anything major. Blood, urine, the usual. It could save a lot of time and money. I hope you're babies okay!
I'm never having children. I have two cats. Sisters no less.