Please do post when you find out what tests were run and what the results were.
Metronidazole is often used to treat diarrhea even if no giardia is found - it helps to soothe the gut and 'resets' it. Giardia can be really tricky to find.
Flea drops take some time to work - they aren't instant, so Lola probably picked up some new fleas in the environment and they hadn't been killed of yet, the original application was still effective so an early reapplication was unneeded until the next scheduled day. Many pets are still sensitive and may remain itchy even with proper treatment. This usually resolves with time, as the skin heals.