3 year old loose poos

[Worryismything]

My son is 3 and a half and recently has been having loose poos (not watery but mushy)
He has been toilet trained for about a month now, but his poos are loose enough for him to not realise he has done them, or will trump and poo will stain his pants.
His diet hasn't changed and it seems to have come from nowhere, he is ok majority of the time in himself, but I am worried about what it could be.

I am going to phone the Dr's tomorrow to get him checked over, but has anyone had similar with their little ones?

He has had this for 2 weeks now, so kind of ruling out it being a bug....only thing I can think of that has changed, is he had a pre school injection a month ago.
He also seems OK in himself other than he has just woke up crying and clutching his tummy, but has just gone back to sleep

Has anyone been in similar situation?

Hey hope you get some good advice from the doctor. My 3 year old gets this on and off and from what I've read it can be due to their diet having too much carbs and not enough fat. Drinks like fruit shoots or pure fruit juice can also cause this.

Sounds like constipation. The mushy poo, the staining etc could be overflow. If he’s newly potty trained, he could be withholding which is causing the constipation. (Talking from experience with my 3 year old!)

The Dr's have said it could be down to his pre school injections he had last month 🤷🏼‍♀️.
He is fine in himself, and I don't think it would be constipation as he is pooing after every meal or anything he eats pretty much.
And he is pooing frequently and close together