Fast flow or allergy?

Hi, my little boy is 6 months. Around the ago of 4 months he had a tummy bug and since then has had mucusy poos. I've been dairy and soya free for 2 weeks ( dairy free for a month) and he's been on probiotics to try and sort the poos. Yesterday he had a normal breastfed poo and this morning had a really wet loose poo (shiny and excessively wet). But a couple hours later he had a normal breastfed poo again. I was wondering if allergies can go like that where one poo is normal and one is not. I'm thinking the poo this morning could be due to a fast let down as I do have a fast let down anyway and this morning he hadn't fed for 6 hours so I was more full. Is this more likely? Just trying to work out if the dairy and soy free diet is working