💩 photo sorry!! But worried mum…

4 month old formula fed has had some mucus in his poo a few times in the last week or so, same colour as his poo and not every time. He’s been drooling a lot/has been congested so I wasn’t overly worried when I looked into it. However I’ve just changed his nappy and there is now this dark mucus (i think it's mucus) which I haven’t seen before? Should I be concerned? My GP isn’t great at appointments so just wanted to check first if anyone has seen similar? he seems ok in himself in generally and doesn't have a temp…