Guys who have been on T for a few years often experience some breakthrough bleeding. I'm not sure anyone has ever been able to nail down a cause.
Had you had any issues with shark week prior to this? Could it just be a random period? Does it look like a period or does it look different? Other than bleeding, how do you feel?
I would make an appointment with the doctor that prescribes your T at the very least. If it continues, causes you pain, or doesn't look like a period then I might consider going to urgent care.