I swapped Dogmeat for Codsworth as a companion at Sanctuary Hills and 'sent' him to Sanctuary Hills.

Couple of quests later, I returned back to Sanctuary Hills and I have spent a good 15 minutes looking everywhere trying to find Dogmeat in Sanctuary Hills.

I even built doghouse and slept 10 hours but still no sign of Dogmeat ;_;

I'm going to give you a pro-tip;

Sanctuary is huge and you will have a hard time finding your companions there. The game has over 20 settlement locations and some are super small/enclosed/whatever (one even looks like a pre-war town...kinda). It's best to nab one of those locations for your companions (just don't setup a recruitment beacon and you'll never have to deal with providing food or defenses or anything as there will technically be no settlers there).

I've got all my companions chilling at Covenant.

Thanks for the tip but that's not what I'm really here for, the problem is that I can't find Dogmeat anywhere in Sanctuary Hills where I sent him to.

What if I sent Codsworth to a settlement and he'll disappear too?

I only have three settlements unlocked at the moment.

I found Dogmeat, he was sitting in a doghouse behind a yellow house surrounded with bushes with truck out in front with a bit of red paint on it. The house is at the end of the road.

He was quite well hidden from me