I have had a numb big toe for about 4 months now (i'm 18 year old female). there are no other symptoms at all. numb from the last joint. ideas?

Small nerve: Most likely cause is damage to one (or more) of the small nerves which run into each toe (digital nerves). Compression is the most common cause, often by shoes. If no obvious compression, then maybe see a podiatrist for starters.

Numb Big Toe: There are four branches of nerves that enter the big toe. Irritation and pressure from shoe gear and abnormal foot function can produce trauma to the branch that becomes numb. Expensive shoes are not always good shoes especially if they're not fitting your feet properly. Your podiatrist and examine your feet take x-rays and perform a biomechanical examination to determine causes of your numbness.

Ideas would be: 1) check shoes for proper fit. 2) numbness may be caused by a pinched nerve in your back. 3) you may have a vitamin deficiency. I would check out those ideas first.