Thank you for asking your query.
I assume you had unprotected (without condom). In that case you do have some risk of contracting HIV. The symptoms after 12 days might not be related to HIV. But in rare cases HIV infection can cause early symptoms called - Acute Retroviral Syndrome, which can have the above symptoms.
I recommend you to get tested for HIV as soon as possible. I recommend a RT-PCR testing for an early diagnosis. Alternatively you can visit a VCTC (HIV counselling centre of your Doctor).
Chances are that this symptoms could be due to a viral infection (common flu). So there is no need to worry unnecessarily. But these symptoms needs evaluation and HIV testing is a must.
Hope this helps
Please feel free to ask followup questions.