Does a 5 month old fully breastfeed baby still poo many times a day? Or is it a diarrhoea? Earlier on baby was pooing only once every 2 to 3 days. This week itself baby is pooing 2 to 3 times each day.

I would be more concerned that it's diarrhea if the poo is more watery than usual rather than the increased frequency. Breastfed babies' poop frequency has a really wide range compared to fm fed babies. I'd also check that baby's not dehydrated, (no of wet diapers is the same, pee is not dark yellow or foul smelling and if there's presence of dry lips etc) and has no fever or lethargy, as these are really clear signs that warrant a visit to a doctor.