It's quite hard to get, even if you have unprotected sex with an infected person. That said, it's so potentially devastating that the low chances shouldn't defer anyone from using proper protection.
Anyway, so you had (presumably) unprotected sex over 6 months ago and are now panicking because you have some very non-specific symptoms. I think it's highly unlikely the two are connected, and it doesn't sound like a stereotypical HIV presentation anyway. Clearly you're worried though, so for your own peace of mind go and get tested (for all STIs, not just HIV).