I'm at week 3 out of 6 weeks iv antibiotic for staph. no fever, labs are good. might i still be tired & achy from the infection?

Yes indeed: Any staphylococcal infection serious enough to require 6 weeks of IV antibiotics almost certainly could cause continuing aches, fatigue, and so on for several weeks. With your fever gone and routine lab results improving, this doesn't sound serious. But of course you should discuss it with the doctor(s) in charge of your care. Best wishes for continued recovery.

Yes.: If you needed 6 weeks of IV antibiotics, then you had a very serious infection. Fatigue is common and may last for a few more months, even after the infection is gone. Eat properly, rest properly and be patient with yourself. Good luck.