Why might this be ?

Usually I poop once every couple of days. And lately I’ve been feeling sick in the stomach and some days I poop a few times in that one day. A lot of the time it’s like runny (like diarrhoea) and it’s not after certain foods it just happens all the time.

I thought it was because of milk because I’d get up and have a milk drink ( tea or coffee or whatever) and I’d feel sick after but it’s just after basically everything now. Like I can’t pinpoint anything