What Causes Yellow Vaginal Discharge?

I have not had a period for 15 years. I have a yellow dischage that also has pieces around the vagina that look like pieces of toilet paper also with yellow tint. no itching. I notice thiscouple days after going to bed with my boyfriend. His dogs sleep with him and I may been sleeping in some dog dander. Do not know if this is of concern. I used tea tree oil for the first two days and it was working but was afraid to use it further incase I have to have it checked out and may mess up the test results. I has been 5 days since I notice this.