Dog transferring worms?

Once my dad told me you can't let a dog lick you in the face as if they have worms there is a possibility you go blind. My puppy is constantly picking up things he shouldn't and I am taking them from his mouth when they are covered in his drool. He gets de wormed every 3-4 months. Normally I wash my hands before eating etc but this time I completely forgot as I was crying lots today so I ate food even though I probably had dog slobber all over my hands. When he goes to the toilet I never see anything. Is it ok then? But he keeps on alternating between constipation and diarrhoea (one time I saw blood as well) is this because he is a puppy so his stomach is adapting?