Are you in the US?

You should obviously take this up with your builder - they are the responsible party for resolving these issues.

That said, it's helpful to go in with some facts so they don't pat you on the head and tell you it's fine.

-Humidity: Measure it and record it inside and out daily for a week or two. If there's a problem, it will be very clear.

-Major leaking?: As in water through the roof, wall, floor, what?

-Vent shut on water heater: I would need a detailed explanation on that. A gas valve off, that I would believe. A vent closed.... there shouldn't be a damper on an appliance vent.

-Fruit Flies, sulfur smell in laundry, sound of air blowing in sink: These COULD be related.

I assume you have run some water in every sink / shower / tub / etc. Water in the trap prevents sewer gases from entering the building. I would have thought that every plumbing fixture was tested (and thus water in the trap) but perhaps not.

Make sure if you have a floor drain, a laundry pan drain, a laundry sink drain, etc. that you pour some water in all of them.

- In your master sink: Use smoke to see if there is air coming out of the sink drain when the AC is on. Use incense, a cigarette, a smoke candle, etc. If you have air coming out of your drain you have a problem.

If the sulfur smell continues (rotten egg smell) there can be other causes - but lets rule out sewer gas because the traps don't have water in them first.

Hard to believe every vent in the house was done wrong but everything you said point's to improper vent and/or trap. If it was my 2 week old house I'd be talking to the builder. Why in blazes haven't you asked the builder to look at it?

Are you on a well? Hydrogen sulfide can be a result of that. Does your hot water smell too? HS can build up in the water heater.

Fruit flies live off more than just fruit. I've had infestations that persisted living off trash, dogfood, etc.

It sounds to me like you may have a case of drain flies. Since you have a sewer gas odor - do you have a floor drain in the laundry that may be dry? The flies could also be nesting in drains where the p-trap is functioning properly.

One possible remedy: Pour in 1/2 cup of salt
and 1/2 cup of baking soda plus a cup of white vinegar. Allow it to work
its magic overnight then flush the drain with hot or boiling water the next morning. This will sanitize the drain and kill the flies and their eggs.

Awesome, thank you. we figured out the sewer gas smell. A cap wasn’t reinstalled when they were working on the hot water heater. 👍🏻 Appreciate your advice.

Agree that you may have drain flies, not fruit flies. They look pretty much the same but are there for different reasons ;0) To test, you could put tape like painters tape over a drain (sink, shower, tub), check the next day and see if any are trapped on the sticky side to confirm not fruit type, and not the gnats that breed in houseplant soils (another pest found in potted plants called fungus gnat but most wouldn't know the difference looking only at the gnat/fly).