When i press down on waist i feel like vomiting and have sharp pain.what could it be? not sexually active so std not an option.

Abdominalpain/nausea: You need to be seen and examined by a doctor ASAP. This could be your gall bladder, a peptic ulcer, or any of a dozen other issues. Do not wait until you become critically ill. Go now and get seen, in an ER if necessary.

Many things...: Its not possible to tell you exactly what is causing your symptoms without an exam and some tests. A large ovarian cyst with torsion (and many other things) could cause symptoms like yours. See your doc and find out. Best wishes!