Loose mucus stools

My son is 5 weeks old today and he has a lot of trouble having dirty nappies. You can tell he is in a lot of discomfort and sometimes need his legs held to help. When he does go he has very loose motions almost runny and now they are a mucus like consistency. I took him to get checked today as his stomach is quite distended and I can't bare seeing him in so much pain. It was a stand in Dr I've never met and first question was I a FTM. He said I was basically overreacting and it can be normal for a baby to go 8 days without a dirt nappy?!!

So he dismissed my concerns and said it was nothing but I can't help but think a baby in pain is nothing and mucus stools does not seem normal. Has anyone any experience with this or any advice? He is formula fed.