These are very none spacific symptoms and aren't STD related at all. Unprotected oral sex is pretty safe especially if it was only 20 seconds so I wouldn't even get tested from this unless real symptoms occur ie burning urination or discharge from the penis. I think your guilt about this event is causing you more concern than any STD.
Guilt stds are the absolute worst. I haven't found a cure for guilt yet.
Go ahead and get checked out if you think that will put your mind at rest.
If it's been >6 weeks you can test for most things and get somewhat accurate results.
If you figure out what it is, let us know.
I think when we cheat our partner (I talk from my personal experience) is our dutty to protect her. And one way to protect her is to test.
In the following chart you can find the risks of insertive oral sex:
Herpes is very easy to transmit and may be asymptomatic, so you should take a look to that specially.
All the best.