Definitely sounds like an anxious state of mind. Anxiety is treatable. Oral sex carries with it a low risk. And symptoms for std's don't start the next day like you describe or follow a pattern like that.
Greetings.
Your symptoms are inconsistent with any STI but they suggest you are very anxious.
Itchy scrotum on day 4 and pimple on day 3 were not caused by STIs.
Since we don't know what day 5 ans 6 can bring you, you should seek help for anxiety issues