I have a simple cyst on my left ovary size is 6x4, I had a transvag u/s 2 weeks ago and still have severe pain did vomit once could it have burst?

Yes, go to ER! I'm so sorry you're going through this. Definitely it could still be there, or it could have ruptured, either is possible. Pain and vomiting can also be a sign of ovarian torsion.... Which is something that needs immediate surgical attention. I recommend that you go to the er for evaluation now... In the event that you have this condition your doctors need to know. Best of luck to you!