Reoccuring 1 canker sore in the same spot, i got tested for herpes 2 months ago and they came back negative, what is it?

Canker sore : Canker sores are the most common oral lesions. Individual ulcers typically last 1-2 weeks. The condition is idiopathic (cause is not known) recurrent aphthous ulcers is usually self-limiting. Try to keep adequate oral hygiene as possible. If concerned see your dentist after 10 days or visit today for laser immediate amelioration.

Lichen Planis: There is an auto-immune disease called Lichen Planis that has many types of stages, lesions and outbreaks. Since you have other skin conditions, you may want to talk to a dermatologist and your dentist concerning your sores. Good luck.