You should take no test. You were never at risk.
Rashes are caused by all kinds of things, including allergies. If you're concerned about STDs, you should get tested.
No. As you were advised 3 weeks ago, oral sex does not pose a risk. Neither does fingering. In adults, HIV can be acquired through penetrative, unprotected genital or anal sex, or by sharing IV works with an HIV-infected drug user.