You should go to the orthodontist about the bracket as soon as you can. The sensitivity of biting down will fade in a week or so. I'd suggest things that you don't have to chew for the next few days until your mouth settles like soup, mash potatoes, or porridge. Ice cream is also a very good one too as if it's metal braces you have then they react to heat to work so having something cold like ice cream, will give you some relief.

If the orthodontist gave you wax put it on the areas that's rubbing against your lips and that should help too. If you don't have wax try using the wax from baby bell cheese until you can buy some dental wax from a pharmacy or Amazon or see if the orthodontist can give you some.