I took a 2/3 day course of antibiotics for a UTI last week (Thu-Fri) and have been feeling noticeably very tired since the Sat/Sun, with mild on-off nausea. Could the antibiotics still be causing this despite finishing them a week ago? The other unlikely possibility is pregnancy, although I'm only 10 days post ovulation today - surely too early to have been experiencing nearly a week of tiredness and nausea?