I have a small tender lump between my anus and vagina what is it??

Very hard to say: Without examining you it is very hard to say what this is, but a short list would include an external hemorrhoid (most likely since this is painful), a skin tag, or if you've had vaginal deliveries with any tearing this could be a keloid (inflammatory scar) from a vaginal laceration repair.

Lump: This could be a number of things, including just a skin fold, but since it is tender, that is a sign of something abnormal. I recommend you have it examined by your doctor to rule out infection.