Dr prescribed antibiotics (keflex) for possible secondary infection from flu. been on them for 2 days and now feel worse?! is that normal?

Well that depends: The awfulness of influenza usually peeks around day 2-3 of symptoms and persists for a good 5-7 days. So if your flu is just reaching it's normal peak, then yes, I'd say your worsening is expected. If you're past that peak though, worsening would not be expected. If the concern is a secondary pneumonia or bacterial sinusitis following flu, keflex is not a standard treatment for either.