Thanks for your query at DoctorSpring. I can understand your concern.
If the HIV tests are negative even after 6 months, then they are accurate.
Window period is usually three months after exposure.
I would recommend that you visit your doctor who can order blood tests for you like complete blood count, liver profile, kidney profile etc.
There is probably some other reason for your symptoms.
You could send me a picture of your rash, which I can have a look and suggest to you what is the rash due to.
P24 antigen assay is usually confirmatory test for HIV , however in case your doctor feels the need to repeat a test for HIV after he examines you and does the other blood tests, he would advise you accordingly.
Hope I have answered all your queries. Please feel free to discuss further.