Insist, if your mommy-senses goes on alert, that they test a stool sample so that you can know if it is just a runny tummy or if it is a more serious viral or bacterial or whatever type of infection and don't just take antibiotics. We had a stool sample taken with my LG and it was only when they found out that it was a parasite that she'd gotten and got the right meds when she got better.
The tummy will probably still be runny – diarrhoea is usually self limiting, it will probably start to improve within the next one to three days. Make sure you have a good nappy rash cream (like some zinc and castor oil ointment) for that sensitive skin.
When you give the probiflora, make sure it's one hour AFTER the antibiotic! A lot of pharmacy personnel forget to advise that.
The best thing for a runny tummy in a little one is Oral Rehydration Solution. You can make up your own with a litre of water, 6 teaspoons of sugar and a half a teaspoon of salt or you can buy sachets at your pharmacy/supermarket (rehidrate, ceralyte, etc.). You can also give probiotics such as Reuterina drops. As long as he doesn't have a fever or isn't miserable then you should be fine.
Don't give anything to block up the tummy! If the diarrhoea persists, I'm pretty sure that you can also give him some Tasectan or Smecta which protects the intestinal lining.