you have to show that the alleged malpractice fell below the standard of care, and that the alleged malpractice led to specific damages. If your damage is only that you waited in pain and had two ER visits the case may not have sufficient damages to be worth pursuing. If the waiting caused additional surgeries it may be worth pursuing. You may want to contact the hospitals that you went to the ER in and request your medical records. It is possible that they did everything they were supposed to but that the clots had sufficiently developed by the third time.
There are multiple issues that need to be evaluate for a successful medical malpractice case. You may have a case, but you might also not have a case that is monetarily worth pursuing.