Baby having no solid poos

[ReturnofSaturn]

Hi all. For the last few weeks my 9 month old has not had a solid bowel movement. They have all been yellowy and like diarrhoea.
He's eating fine still and otherwise seems ok in himself...should I be concerned?

Bump

Has he recently had an illness or a change in milk?

No no change in milk. He had his first tooth come through a few weeks ago but that's it.