Hi.
Thanks for your query and an elucidate history.
Read and understood the whole history.
Since there was no penetrative sex and there was no
injury on the penis you can no get
HIV or Hepatitis C.
Stop worrying.
Now the questions:
1- Assuming that she is HIV+ or hepatitis C, can she transfer the virus to me if there was any vaginal secretion on her underwear to my bare penis?
If there is no injury or cracks on your penis, you can not get any HIV or Hepatitis C.
2- Can the HIV or
hepatitis C virus exist on my penis till I ejaculated then go inside my body through my semen?
No, this never happens and not reported to occur in such a way till now.
3- Do I need to do any kind of test?
No tests are needed at the moment.
You can see if you have any symptoms, then consult a Doctor, get examined and then only tests may be needed.
I am sure these answers clears your doubts.