With a new home it's likely that you have some sort of homeowner's warranty in effect. Even if you didn't sign one, or the builder didn't specifically offer one, many states have laws that put them into effect by default.
Document your problems. In detail. "The floor sounds like it is falling" won't cut it.
Try "When walking across the living room floor, which is oak hardwood, the floor feels unsteady underfoot. It feels as though the floorboards are moving up/down 1/8" or so. The floor makes a clicking/popping noise when walking across it. The noise occurs in the morning/afternon/night and occurs intermittently/continuously. It has gone on since the closing/it just started three weeks ago. Yadda, yadda, yaddda."
The floor may not have been laid tightly, and with the lessened humidity in winter, the boards may have shrunk just enough to allow them to move against each other ever-so-slightly. Increasing the humidity level in the home may help.
Anyhow, document everything. From the lawn to the floors to the drawers that stick to the screw heads that don't line up.
Pictures, dates, descriptions, etc.
Know what you want done about these prolems, and say what you want done. Time bound the builder with a date that you'd like a reply by...say 5-7 business days.
Don't be emotional...be business-like. Being a single Mom with limited financial resources makes you no different from someone with a six-figure income when it comes to getting newly-built homes fixed. You're simply asking the builder to deliver a home in new condition.
If he drags you along time-wise, then offer a reply to the BBB. If still no reply, your options are legal. Either through a lawyer or on your own via small claims court.
Know what's wrong. Know what you want done about it. Know the timeframe in which you want it done. Document, document, document.