On my lower back i have a dark red kind of purplish mole with uneven edges that appears and disappears from time to time, could it be bad?

If a lesion: Disappears, likely it's benign. Your description of the skin mole sounds like telangiectasia, small capillaries/ blood vessels. See your dr for any concerns & for accurate diagnosis.Take care!

Sounds vascular: It sounds like it is some form of blood-vessel related growth, like an angioma or hemangioma, rather than a typical "mole". How large is it? Is it raised? How long have you had it? Without a photo, it's hard to tell by your description - see a dermatologist for a definitive diagnosis.