poorly baby

[Mimzey15]

My nearly bf 12 week old had a water nappy on Sunday morning but didn't have any more after that. Then yesterday (Tuesday) he had a green mucus nappy and then tiny bits of green mixed in with his normal nappies. He woke 30 mins ago and has just had another watery nappy....even got the wall...so I'm wondering if k should get him checked out. My only concern is if they ask for a stool sample? How do I get it and what do I put it in? Any help gratefully received - worried first time mommy