I did a vinegar jar spell on my lovers girlfriend. I didn't want to cause her harm, just wanted her to feel our pain. I'm afraid the spell turned on me instead. The day after I cast the spell my lower back has been causeing me so much pain. I did release her from the spell today. What can I do to be sure the spell didn't turn on me or to break the spell.
Well, a good thing to do is check to see if the work should've been done, or was justified. You should have divined with the spirits in some way to check that. Because Vinegar Jars along with other workings from this tradition (Honey Jars, for instance) don't backfire.
A Vinegar Jar sours someone's life. This can take effect in a variety of ways, and can be harmful. Did you state exactly what you wanted to happen?
How did you "Release her from the spell?" Did you dispose of it in anyway? I would also take some sort of cleansing bath in some purifying herbs (air dry, no towels) just to get rid of any negativity that may linger around me.