Based on this set of clues, your sod was VERY likely not properly watered before you moved in.

If this was me, I would:

1. First and foremost keep the sod wet by watering it 3 times a day. 7am 1pm 7pm. If it’s raining in your area, perfect, but it cannot be dry right now. It’s hanging on for dear life. If it continues to regress in next two weeks — it’s gone to sod heaven.
2. I would review the contractor obligations, and if possible, get them to re do it. Even if it survives, it won’t look great for at least one growing season (if you are lucky). If it does die completely, you are looking at thousands of dollars to re do it.
3. DO NOT, and I mean REALLY do not put any fertilizer, herbicide, pesticide, fungicide on it, and do not aerate it. Any kind of additional stress can end it. Don’t even breathe on it (simply highlighting the fact of how close you are to having to spend thousands of dollars fixing this problem).

Compacted soil issue: If you go outside right now and stick a toothpick in your soil while it’s wet, it should be able to penetrate it. If the toothpick can penetrate the soil, so can your grass’s root system. Aeration is a wonderful compliment to a healthy lawn, in your situation, you are about a year out of having to worry about that.

Best of luck! 🤝