If i went to the hospital because i was very ill without knowing the cause and they did blood work would they usually test for an std?

Not necessarily: This depends on the clinical picture of "very ill" The most pertinent information regarding std's is carried out with a pelvic exam. Don't forget that your medical record is YOUR record. You can get a copy of this from the hospital with a request. If you have symptoms persisting, then I would followup as an outpatient with a visit to address them.

Std: Depending on why you went to the hospital they would not necessarily test you for an STD- but if you are worried, you should please request testing