A smudge stick is a bundle of dried herbs, usually bound with string into a small bundle. The herbs are later burned as part of a ritual or ceremony. Sage is used to rid of negative energy, particularly in the home.
How did the negative energy come to be in your house?
Negative energy can come from a lot of sources. There may have been a lot of stress or unhappiness in your life before. This energy can build up and start to manifest as negative energy in the house. It can be one person in the house who is unhappy or destructive to themselves or others that attract the negativity.
The previous owners or tenants may have suffered great losses or had periods of distress and uncertainty. When you moved into the house that energy was already there.
If there's a lot of loneliness or longing you can attract ghosts. Some of these spirits can be quite negative and troublesome.
It can be related to your work. If you're a healer, a nurse or therapist you help people release pain and suffering everyday. And some of that energy can follow you home and build up in certain areas of the house.