How long or how many days does penicillin or antibiotics last in the body or blood stream after you stop taking them?

Different for each. This varies widely, from a few hours (e.g. most oral penicillins, like amoxicillin) to around 10 days (e.g. azithromycin). The quinolones (e.g. ciprofloxacin) and tetracyclines (e.g. doxycycline) typically are gone in 2-3 days.