Aptamil diarrhoea

[Zulu32]

My DD is 7 months old and has been on Aptamil since she was 5.5months (prior to that she was exclusively BF). All was well until last weekend she had terrible diarrhoea, so much so that it was exploding out and soiling clothes. Every poop!
We went to the doctors because she had loss of appetite and he said it may be a bug or lactose intolerant. So we changed to Aptamil lactose free and it seemed to have stopped.
However, I also developed diarrhoea, so we put it down to a bug.
The lactose free gave my DD terrible constipation! It was horrible to see my baby is so much pain, trying to pass a stool!
We switched back to the normal Aptamil and the diarrhoea has started again.
Not sure if this is because of the switching and changing or whether she’s lactose intolerant?
The only threads I’ve found are for newborns but because she’s been on the formula for 1.5months without any issues, I just don’t know what to do?
Trialing and erroring formula is just too expensive!
Anyone had anything similar?
Ive resulted to not leaving the house because of her frequent explosions 😭😭

My LO never got on with aptamil at all, explosions! The same with HiPP milk, we went all around the houses and tried the lactose free and aptamil pepti prescription top. Last ditch attempt and some advice from a paediatrician we ended up on Nannycare goats milk which he thrived on but it was soooo expensive so as he got a little older we transitioned to kendamil. The only connection we could find was that all of the other milks were made from skimmed milk, whereas Nannycare and Kendamil are whole milk based. It could be a total coincidence but the skimmed milks went straight through him. He’s transitioning to full cows milk slowly now and seems fine on that too. Thankfully Kendamil was one of the cheapest formulas which was rather nice too.

It is unlikely to be a lactose intolerance as breast milk is high in lactose and you would have had symptoms when breastfeeding.
It could be a cows milk protein allergy in which case you need a dairy free formula. The initial formula are cows milk based but with the proteins partially broken down. The most common milks are pepti or nutramigen. I would go back to the GP for a trial of the formula.

Thank you!
so far she’s been alright and been having solids 🤷🏼‍♀️.
Im thinking she was just getting over a bug. I’ll keep an eye on it and anymore flare ups, I’ll go back to the docs 👍🏽