Your situation involves having a bit of a panic attack that you are hiv positive and continuing to worry, despite getting a negative test result. No worries, these tests are accurate so you should move on.
You are thinking the nurse does not know how to do her job PLUS you think that you figured out how she should have done it despite not having any medical training. That doesn't really make any sense, so you should accept the test result just like you would accept any other medical test and forget about this non event.
You know what seems to be being missed here? REGARDLESS of the test, you never put your child at risk any way. They can get your blood in their mouth and it is NOT a risk for HIV. Air and saliva inactivate the virus. Also, you don't think it is a little bit odd that you all of a sudden wonder if you actually have HIV? That really does sound like irrational and anxious thinking. If you've never tested before then fine, take a test. But it is most likely negative and you could not transmit HIV through your child getting your blood in their mouth any way.
If you have episodes like this often where you fill with worry over what is hard to make sense of as to why, then seek help for anxiety.
I'm sorry to be redundant since your questions and concerns have been more than adequately answered. I CAN understand your concern considering all the fear surrounding COVID......while these issues (HIV/, COVID) are not related, it has, unfortunately, brought back the fear/paranoia/panic of the AIDS scare during the 80's. I just wanted to also reassure you that your son had zero risk of contracting HIV from this situation.....even IF you were HIV+ I'm with GuitarBox on this one, thinking it's more of an anxiety issue that you need to deal with. Getting tested, which we all believe is unnecessary in this case, is an option for you to gain some much needed peace of mind so you can move on. If your negative result (which I'm sure it will be) does not curb your anxiety, your next step would be to seek therapy. Your son may only be four years old, but don't think they can't pick up on anxiety at that age. Do whatever you have to for BOTH of you.
You were never at risk. Condoms protect against transmission of HIV. Oral is not a risk. Therefore, you are not positive at the first place to transmit this virus to your child.
Hypothetically speaking, even if your child ingested some amount of infected fluid, there is no level of risk associated, since it is not the right route to transmission. Presence of saliva and gastric acid inhibits the virus.
You are being paranoid and it will be a good idea to discuss this with a therapist to overcome such irrational worries.