Thank you for the additional information.
There are a couple of options in this situation.
The only way to get Seroquel would be to get a refill from your doctor or to see another doctor. If you need medicines before your doctor is available again, then you would need to be seen, either in a Emergency Room or an Urgent Care Center. None of the symptoms that you are having are emergencies, of themselves, but if you are feeling more miserable from the symptoms, then it would be reasonable to be seen in an ER or Urgent Care Center.
If you would rather try to manage these symptoms at home, there are a couple of options of over the counter medicines that may be able to help. There are several pain medicines that may help with the sensation that the head is going to explode, but since you are already having some vomiting, it would be better to use the medicine that is gentle on the stomach, acetaminophen/Tylenol. A first generation antihistamine, such as diphenhydramine/Benadryl may help with the nausea and vomiting, and also may help with sleep. In fact, most of the over the counter sleep medicines contain diphenhydramine. For the diarrhea, it is OK to take Imodium.
Is there any other information that would be helpful?