I would be concerned if you have other symptoms like light headedness, dizziness, breathing problems, or anything abnormal with your menstrual cycle (like heavy bleeding).
If you've got any of the first problems you might have anything from a cold, stress, or the light headed and dizzy are symptoms of migraines if you have those (I've fallen down when a migraine is coming on). Breathing problems could be stress or anxiety related... If you're having anything odd with your menstruation, it could be a lot of things and I would see a doctor - but I would see a doctor if you have any additional symptoms.
A person can be clumsy and off balance for any number of reasons and it can be nothing to worry about. If you don't have anything else going on, I'd just mention it to your doc at your next appointment. If you have other symptoms, I really would make an appointment about it though. Might just be stress or a cold, but it could be something more serious. Something like Meniere's Disease could cause this, though I think you'd be having more severe problems...