Hi StyreneOxide,
You are welcome
So the cold sensitivity is less likely to be a nerve problem, which is good news. The recession of the gum was a gradual thing as the site was healing. So when it reached the point of root exposure, which can be so so tiny, that is when you got the symptoms. The tooth could also have a small fracture, not unusual. However, you stated that you are clenching and under stress... so you could be beating up that tooth without realizing it.
The area where the gum has receded will not grow back. So it is important to keep that area clean so it does not decay. You do not need to be aggressively cleaning it, just treat it like every other area of your mouth and be thorough with the brushing and flossing. If food keeps getting impacted in that area, have your dentist check it to see if he can alter the contact point to prevent food impaction.
It takes about 2 weeks to have a night guard made, although they can ask the dental lab to rush it. So this would need to be considered soon as you may need to have some adjustments to it initially. Your dentist may also be able to apply a desensitizing agent over the sensitive area. This eventually wears off and needs reapplication. But sometimes it can be helpful if only for a short term.
Tooth pastes made for sensitive teeth may be helpful over time as they work by way of a cumulative effect. Not instantaneously.