I'm concerned I have a toe fungus on my right big toe nail. There is a brown spot surrounded by some discoloring. And I can't tell what it is.

Does not. aound like a fungus but see a dermatologist when you can.
Be seen. You would want to be seen for it. There have been occasions where seemingly small lesions can represent a malignant melanoma, so it is important an accurate diagnosis be made.
A podiatrist. or dermatologist can sample the nail and give you a definitive diagnosis.
I.D. it Quickly. Recognizing a toenail fungus can sometimes be challenging, even to the experts. There are tests that can pretty accurately do the job. Early diagnosis and treatment will undoubtedly give you the most efficient results. Once the nail becomes heavily infected, it becomes a matter of time and money.