Canker sore

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​sorry but advice needed! I've had this canker sore over a month. It's super painful and I'm not sure if the brown center or size is normal. I've never had one last this long. I don't want to run to the dr for nothing but im adraid i should go