Hi..thanks for your query
From what you describe , it appears that you are starting to have an eczematous rash
behind your knees. You can apply a mild topical steroid
for a few days on the lesions and have oral anti histaminic tabs if it itches.
I do it think you are showing any symptoms of HIV
due to occurrence of a simple rash.
However , since eczematous / similar rashes tend to be persistent and recurrent, you should consultant dermatologist
to get the appropriate therapy started .
Hope this helps.take care!