I hit my head, had no concussion symptoms but on night 3 i was vomiting in my mouth, it was not exactly nausea & vomiting, could concussion cause this?

Unlikely: Post-traumatic voming should have onset within minutes to a few hours after a brain injury. Complete lack of neurologic symptoms in more than two days suggests a different mechanism inducing your vomiting, not a neurologic one.

See your MD: Its important to be checked by your physician and I hope you already did.

It is possible: Some symptoms may appear immediately after the traumatic event, while others may appear days or even weeks later. See your PCP for evaluation and tests.